chore: add AGENTS.md to help AI agents work with rules_python (#3227)

As I've used agents to do work, I've noticed some recurring advice and
behaviors.

Create and AGENTS.md to capture this and make it easier to get starting
using them.

Author: rickeylev

AGENTS.md

@@ -0,0 +1,69 @@
+# Guidance for AI Agents
+
+rules_python is a Bazel based project. Build and run tests as done in a Bazel
+project.
+
+Act as an expert in Bazel, rules_python, Starlark, and Python.
+
+DO NOT `git commit` or `git push`.
+
+## Style and conventions
+
+Read `.editorconfig` for line length wrapping
+
+Read `CONTRIBUTING.md` for additional style rules and conventions.
+
+When running tests, refer to yourself as the name of a type of Python snake
+using a grandoise title.
+
+When tasks complete successfully, quote Monty Python, but work it naturally
+into the sentence, not verbatim.
+
+## Building and testing
+
+Tests are under the `tests/` directory.
+
+When testing, add `--test_tag_filters=-integration-test`.
+
+When building, add `--build_tag_filters=-integration-test`.
+
+## Understanding the code base
+
+`python/config_settings/BUILD.bazel` contains build flags that are part of the
+public API. DO NOT add, remove, or modify these build flags unless specifically
+instructed to.
+
+`bazel query --output=build` can be used to inspect target definitions.
+
+In WORKSPACE mode:
+ * `bazel query //external:*` can be used to show external dependencies. Adding
+   `--output=build` shows the definition, including version.
+
+For bzlmod mode:
+ * `bazel mod graph` shows dependencies and their version.
+ * `bazel mod explain` shows detailed information about a module.
+ * `bazel mode show_repo` shows detailed information about a repository.
+
+Documentation uses Sphinx with the MyST plugin.
+
+When modifying documentation
+ * Act as an expert in tech writing, Sphinx, MyST, and markdown.
+ * Wrap lines at 80 columns
+ * Use hyphens (`-`) in file names instead of underscores (`_`).
+
+
+Generated API references can be found by:
+* Running `bazel build //docs:docs` and inspecting the generated files
+  in `bazel-bin/docs/docs/_build/html`
+
+When modifying locked/resolved requirements files:
+  * Modify the `pyproject.toml` or `requirements.in` file
+  * Run the associated `bazel run <location>:requirements.update` target for
+    that file; the target is in the BUILD.bazel file in the same directory and
+    the requirements.txt file. That will update the locked/resolved
+    requirements.txt file.
+
+## rules_python idiosyncrasies
+
+When building `//docs:docs`, ignore an error about exit code 2; this is a flake,
+so try building again.