docs: add /ask, /env, MCP registry install, and plugin marketplace update

Document new Copilot CLI features from releases v1.0.25–v1.0.27:
- Add /ask command to Essential Slash Commands (ask quick questions
  without affecting conversation history)
- Add /env command to Additional Commands reference (shows active
  instructions, MCP servers, skills, agents, and plugins)
- Document MCP server registry installation (/mcp install) in Chapter 06
  as the beginner-friendly path before manual JSON configuration
- Add 'copilot plugin marketplace update' command to Chapter 05 plugin
  section so learners can refresh stale plugin catalogs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: DanWahlin

01-setup-and-first-steps/README.md

@@ -363,17 +363,20 @@ copilot --allow-all -p "Review @myfile.py for issues"
 
 ## Essential Slash Commands
 
-These commands work in interactive mode. **Start with just these six** - they cover 90% of daily use:
+These commands work in interactive mode. **Start with just these seven** - they cover 90% of daily use:
 
 | Command | What It Does | When to Use |
 |---------|--------------|-------------|
+| `/ask` | Ask a quick question without it affecting your conversation history | When you want a quick answer without derailing your current task |
 | `/clear` | Clear conversation and start fresh | When switching topics |
 | `/help` | Show all available commands | When you forget a command |
 | `/model` | Show or switch AI model | When you want to change the AI model |
 | `/plan` | Plan your work out before coding | For more complex features |
 | `/research` | Deep research using GitHub and web sources | When you need to investigate a topic before coding |
 | `/exit` | End the session | When you're done |
 
+> 💡 **`/ask` vs regular chat**: Normally every message you send becomes part of the ongoing conversation and affects future responses. `/ask` is an "off the record" shortcut — perfect for quick one-off questions like `/ask What does YAML mean?` without polluting your session context.
+
 That's it for getting started! As you become comfortable, you can explore additional commands.
 
 > 📚 **Official Documentation**: [CLI command reference](https://docs.github.com/copilot/reference/cli-command-reference) for the complete list of commands and flags.
@@ -388,10 +391,13 @@ That's it for getting started! As you become comfortable, you can explore additi
 | Command | What It Does |
 |---------|--------------|
 | `/agent` | Browse and select from available agents |
+| `/env` | Show loaded environment details — what instructions, MCP servers, skills, agents, and plugins are active |
 | `/init` | Initialize Copilot instructions for your repository |
 | `/mcp` | Manage MCP server configuration |
 | `/skills` | Manage skills for enhanced capabilities |
 
+> 💡 **`/env` tip**: Use `/env` whenever you want to confirm that Copilot has picked up your custom agents, skills, or MCP servers. It's a great first step if something isn't working as expected.
+
 > 💡 Agents are covered in [Chapter 04](../04-agents-custom-instructions/README.md), skills are covered in [Chapter 05](../05-skills/README.md), and MCP servers are covered in [Chapter 06](../06-mcp-servers/README.md).
 
 ### Models and Subagents
@@ -653,7 +659,7 @@ The examples used `/plan` for a search feature and `-p` for batch reviews. Now t
 1. **Interactive mode** is for exploration and iteration - context carries forward. It's like having a conversation with someone who remembers what you've said up to that point.
 2. **Plan mode** is normally for more involved tasks. Review before implementation.
 3. **Programmatic mode** is for automation. No interaction needed.
-4. **Essential commands** (`/help`, `/clear`, `/plan`, `/research`, `/model`, `/exit`) cover most daily use.
+4. **Essential commands** (`/ask`, `/help`, `/clear`, `/plan`, `/research`, `/model`, `/exit`) cover most daily use.
 
 > 📋 **Quick Reference**: See the [GitHub Copilot CLI command reference](https://docs.github.com/en/copilot/reference/cli-command-reference) for a complete list of commands and shortcuts.
 

05-skills/README.md

@@ -546,6 +546,14 @@ copilot
 # Install a plugin from the marketplace
 ```
 
+To keep your local plugin catalog current, refresh it with:
+
+```bash
+copilot plugin marketplace update
+```
+
+> 💡 **When to run this**: If you notice that new plugins aren't appearing in `/plugin marketplace`, running this command fetches the latest catalog from the marketplace server.
+
 Plugins can bundle multiple capabilities together - a single plugin might include related skills, agents, and MCP server configurations that work together.
 
 ### Community Skill Repositories

06-mcp-servers/README.md

@@ -119,13 +119,29 @@ MCP makes Copilot aware of your actual development environment.
 
 <img src="images/configuring-mcp-servers.png" alt="Hands adjusting knobs and sliders on a professional audio mixing board representing MCP server configuration" width="800"/>
 
-Now that you've seen MCP in action, let's set up additional servers. This section covers the configuration file format and how to add new servers.
+Now that you've seen MCP in action, let's set up additional servers. You can add servers in two ways: **from the built-in registry** (easiest — guided setup right in the CLI) or by **editing the config file** manually (more flexible). Start with the registry option if you're not sure which to choose.
+
+---
+
+## Installing MCP Servers from the Registry
+
+The CLI has a built-in MCP server registry that lets you discover and install popular servers with a guided setup — no JSON editing required.
+
+```bash
+copilot
+
+> /mcp install
+```
+
+Copilot opens an interactive picker showing available servers. Select one, and the CLI walks you through any required configuration (API keys, paths, etc.) and adds it to your config automatically.
+
+> 💡 **Why use the registry?** It's the easiest way to get started — you don't need to know the npm package name, command arguments, or JSON structure. The CLI handles all of that for you.
 
 ---
 
 ## MCP Configuration File
 
-MCP servers are configured in `~/.copilot/mcp-config.json` (user-level, applies to all projects) or `.mcp.json` (project-level, placed in the root of your project).
+MCP servers are configured in `~/.copilot/mcp-config.json` (user-level, applies to all projects) or `.mcp.json` (project-level, placed in the root of your project). If you used `/mcp install` above, the CLI already created or updated this file for you — but it's useful to understand the format for advanced customization.
 
 > ⚠️ **Note**: `.vscode/mcp.json` is no longer supported as an MCP config source. If you have an existing `.vscode/mcp.json`, migrate it to `.mcp.json` in your project root. The CLI will show a migration hint if it detects an old config file.