Customization library (custom instructions and prompt files) (#57137)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: hubwriter <hubwriter@github.com>
Co-authored-by: Christopher Harrison <geektrainer@github.com>

content/copilot/tutorials/customization-library/custom-instructions/github-actions-helper.md

@@ -0,0 +1,65 @@
+---
+title: GitHub Actions helper
+intro: 'Generate and improve {% data variables.product.prodname_actions %} workflows.'
+versions:
+  feature: copilot
+category:
+  - Custom instructions
+  - GitHub flows
+  - Path-specific
+  - Repository
+complexity:
+  - Simple
+octicon: book
+topics:
+  - Copilot
+  - Actions
+---
+
+{% data reusables.copilot.customization-examples-note %}
+
+The following example shows a path-specific `actions.instructions.md` file that applies only to {% data variables.product.prodname_actions %} workflow files in your repository, using the `applyTo` field. For more information about path-specific instructions files, see [AUTOTITLE](/copilot/how-tos/configure-custom-instructions/add-repository-instructions#using-one-or-more-instructionsmd-files).
+
+````text copy
+---
+applyTo: ".github/workflows/**/*.yml"
+---
+
+When generating or improving {% data variables.product.prodname_actions %} workflows:
+
+## Security First
+- Use {% data variables.product.prodname_dotcom %} secrets for sensitive data, never hardcode credentials
+- Pin third-party actions to specific commits by using the SHA value (e.g., `- uses: owner/some-action@a824008085750b8e136effc585c3cd6082bd575f`)
+- Configure minimal permissions for GITHUB_TOKEN required for the workflow
+
+## Performance Essentials
+- Cache dependencies with `actions/cache` or built-in cache options
+- Add `timeout-minutes` to prevent hung workflows
+- Use matrix strategies for multi-environment testing
+
+## Best Practices
+- Use descriptive names for workflows, jobs, and steps
+- Include appropriate triggers: `push`, `pull_request`, `workflow_dispatch`
+- Add `if: always()` for cleanup steps that must run regardless of failure
+
+## Example Pattern
+```yaml
+name: CI
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: {% data reusables.actions.action-checkout %}
+      - uses: {% data reusables.actions.action-setup-node %}
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - run: npm test
+```
+````
+
+{% data reusables.copilot.custom-instructions-further-reading %}