.github/llm: add reviewer

[gastmaier]

Uses the buildroot docs/manual as the source of truth, discourages full-builds.

Would be useful to provide steps to build only or until a package failure.
e.g., if the ci/cd fails at lxml, how can the agent build it without spanning a full defconfig build?

[pamolloy]

Would be useful to provide steps to build only or until a package failure. e.g., if the ci/cd fails at lxml, how can the agent build it without spanning a full defconfig build?

The build is parallelized based on the number of cores by running make -j $(nproc). If there is a failure the error message will be buried, but a model should be able to find it easily. But you could also just run the single threaded make without -j and then the error messages will be the last things printed.