docs: improve /fleet command description and add tip in Ch07

- Ch 01: Reword /fleet table entry to be more beginner-friendly
- Ch 07: Add callout tip after Idea to Merged PR workflow pointing
  to official /fleet docs

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

Author: DanWahlin

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

@@ -390,7 +390,7 @@ That's it for getting started! As you become comfortable, you can explore additi
 |---------|--------------|
 | `/model` | Show or switch AI model |
 | `/delegate` | Hand off task to Copilot coding agent on GitHub (agent in the cloud) |
-| `/fleet` | Enable fleet mode for parallel subagent execution |
+| `/fleet` | Split a complex task into parallel subtasks for faster completion |
 | `/tasks` | View background subagents and detached shell sessions |
 
 ### Code

07-putting-it-together/README.md

@@ -100,6 +100,8 @@ copilot
 
 **The key insight**: You directed specialists like an architect. They handled the details. You handled the vision.
 
+> 💡 **Going further**: For large multi-step plans like this, try `/fleet` to let Copilot run independent subtasks in parallel. See the [official docs](https://docs.github.com/copilot/concepts/agents/copilot-cli/fleet) for details.
+
 ---
 
 <details>