Add article about customizing GitHub Hosted runners (#18761)

* add /actions/guides/customizing-github-hosted-runners

* fix linters

* fix comments

* Update customizing-the-github-hosted-runners.md

* customizing-the-github-hosted-runners

* Update about-github-hosted-runners.md

* Added content design updates

* Added misc edits

* Update customizing-the-github-hosted-runners.md

* Small edits to intro

* omit the from title

* Update customizing-github-hosted-runners.md

* Apply suggestions from code review

Co-authored-by: Sarah Edwards <skedwards88@github.com>

* Update customizing-github-hosted-runners.md

Co-authored-by: Martin Lopes <martin389@github.com>
Co-authored-by: skedwards88 <skedwards88@github.com>

Author: 3 people

content/actions/learn-github-actions/migrating-from-circleci-to-github-actions.md

@@ -443,7 +443,9 @@ jobs:
           path: vendor/bundle
           key: administrate-${{ matrix.image }}-${{ hashFiles('Gemfile.lock') }}
       - name: Install postgres headers
-        run: sudo apt-get install libpq-dev
+        run: |
+          sudo apt-get update
+          sudo apt-get install libpq-dev
       - name: Install dependencies
         run: bundle install --path vendor/bundle
       - name: Setup environment configuration

content/actions/using-github-hosted-runners/about-github-hosted-runners.md

@@ -93,6 +93,10 @@ We recommend using actions to interact with the software installed on runners. T
 
 If there is a tool that you'd like to request, please open an issue at [actions/virtual-environments](https://github.com/actions/virtual-environments). This repository also contains announcements about all major software updates on runners.
 
+#### Installing additional software
+
+You can install additional software on {% data variables.product.prodname_dotcom %}-hosted runners. For more information, see "[Customizing GitHub-hosted runners](/actions/using-github-hosted-runners/customizing-github-hosted-runners)".
+
 ### IP addresses
 
 {% note %}

content/actions/using-github-hosted-runners/customizing-github-hosted-runners.md

@@ -0,0 +1,92 @@
+---
+title: Customizing GitHub-hosted runners
+intro: >-
+  You can install additional software on GitHub-hosted runners as a
+  part of your workflow.
+product: '{% data reusables.gated-features.actions %}'
+versions:
+  free-pro-team: '*'
+  enterprise-server: '>=2.22'
+type: tutorial
+topics:
+  - Workflows
+---
+
+{% data reusables.actions.enterprise-github-hosted-runners %}
+
+If you require additional software packages on {% data variables.product.prodname_dotcom %}-hosted runners, you can create a job that installs the packages as part of your workflow. 
+
+To see which packages are already installed by default, see "[Preinstalled software](/actions/using-github-hosted-runners/about-github-hosted-runners#preinstalled-software)."
+
+This guide demonstrates how to create a job that installs additional software on a {% data variables.product.prodname_dotcom %}-hosted runner.
+
+### Installing software on Ubuntu runners
+
+The following example demonstrates how to install an `apt` package as part of a job.
+
+{% raw %}
+```yaml
+name: Build on Ubuntu
+on: push
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out repository code
+      uses: actions/checkout@v2
+    - name: Install jq tool
+      run: |
+        sudo apt-get update
+        sudo apt-get install jq
+```
+{% endraw %}
+
+{% note %}
+
+**Note:** Always run `sudo apt-get update` before installing a package. In case the `apt` index is stale, this command fetches and re-indexes any available packages, which helps prevent package installation failures. 
+
+{% endnote %}
+
+### Installing software on macOS runners
+
+The following example demonstrates how to install Brew packages and casks as part of a job.
+
+{% raw %}
+```yaml
+name: Build on macOS
+on: push
+
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+    - name: Check out repository code
+      uses: actions/checkout@v2
+    - name: Install GitHub CLI
+      run: |
+        brew update
+        brew install gh
+    - name: Install Microsoft Edge
+      run: |
+        brew update
+        brew install --cask microsoft-edge
+```
+{% endraw %}
+
+### Installing software on Windows runners
+
+The following example demonstrates how to use [Chocolatey](https://community.chocolatey.org/packages) to install the {% data variables.product.prodname_dotcom %} CLI as part of a job.
+
+{% raw %}
+```yaml
+name: Build on Windows
+on: push
+jobs:
+  build:
+    runs-on: windows-latest
+    steps:
+      - run: choco install gh
+      - run: gh version
+```
+{% endraw %}

content/actions/using-github-hosted-runners/index.md

@@ -11,6 +11,7 @@ versions:
 {% data reusables.actions.enterprise-github-hosted-runners %}
 
 {% link_in_list /about-github-hosted-runners %}
+{% link_in_list /customizing-github-hosted-runners %}
 {% link_in_list /about-ae-hosted-runners %}
 {% link_in_list /adding-ae-hosted-runners %}
 {% link_in_list /using-ae-hosted-runners-in-a-workflow %}

content/github/authenticating-to-github/adding-a-new-ssh-key-to-your-github-account.md

@@ -87,6 +87,7 @@ After adding a new SSH key to your {% data variables.product.product_name %} acc
   If your SSH public key file has a different name than the example code, modify the filename to match your current setup. When copying your key, don't add any newlines or whitespace.
 
   ```shell
+  $ sudo apt-get update
   $ sudo apt-get install xclip
   # Downloads and installs xclip. If you don't have `apt-get`, you might need to use another installer (like `yum`)