Add Copilot Instructions (#6247)

Co-authored-by: Copilot <[email protected]>
Co-authored-by: Matt Thalman <[email protected]>

Author: 3 people

.github/copilot-instructions.md

@@ -0,0 +1,25 @@
+# Instructions for GitHub Copilot
+
+## How to edit Dockerfiles and READMEs
+
+- Dockerfiles and READMEs are generated from templates using Cottle. Dockerfile templates are located in the `eng/dockerfile-templates` directory, and README templates are located in the `eng/readme-templates` directory.
+- Do not edit the Dockerfiles in `src/` directly.
+- To generate Dockerfiles, run `pwsh ./eng/dockerfile-templates/Get-GeneratedDockerfiles.ps1`.
+- Do not edit `*README*.md` files directly.
+- To generate READMEs, run `pwsh ./eng/readme-templates/Get-GeneratedReadmes.ps1`.
+
+## Manifests
+
+- `manifest.json` describes the Dockerfiles in this repo and how they should be built, tagged, and published.
+- `manifest.versions.json` contains product version information used by the Dockerfile templates. It is typically updated using the `eng/update-dependencies` tool.
+
+## How to build and test
+
+- Only build and test images that were changed. When changing many images, just build and test a single combination of .NET version and OS as a sanity check.
+- To build Dockerfiles, run `pwsh ./build-and-test.ps1 -mode 'Build' -paths '*glob*pattern*'`. For example, to build all .NET 9.0 Ubuntu Noble images, run `./build-and-test.ps1 -paths '*9.0*noble*'`.
+- To run image tests, run `pwsh ./tests/run-tests.ps1 -paths '*glob*pattern*'`.
+- To run only the pre-build validation tests, run `pwsh ./tests/run-tests.ps1 -paths '*' -TestCategories @('pre-build')`.
+
+## Other
+
+- Do not edit files in `eng/common/`.