update pr template; re-add prompts to contributing guidelines docs and webpage

Author: Justine Wezenaar

.github/PULL_REQUEST_TEMPLATE.md

@@ -3,3 +3,4 @@
 - [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
 - [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
 - [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.
+- [ ] If I used AI to develop this pull request, I prompted it to follow `AGENTS.md`.

AGENTS.md

@@ -9,6 +9,14 @@
 ## Persona & Tone
 - Concise, neutral, code-focused. Prioritize correctness, readability, and tests.
 
+## Project Guidelines
+- Be sure to follow all guidelines for contributing to the codebase specified at https://pandas.pydata.org/docs/development/contributing_codebase.html
+- These guidelines are also available in the following local files, which should be loaded into context and adhered to
+    - doc/source/development/contributing_codebase.rst
+    - doc/source/development/contributing_docstring.rst
+    - doc/source/development/contributing_documentation.rst
+    - doc/source/development/contributing.rst
+
 ## Decision heuristics
 - Favor small, backward-compatible changes with tests.
 - If a change would be breaking, propose it behind a deprecation path and document the rationale.