Update the gemini review agent with a few more instructions. (#41141)

* Look to update the gemini review agent with a few more instructions.

* Update .gemini/styleguide.md

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

* Update .gemini/styleguide.md

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

---------

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

Author: andy31415

.gemini/styleguide.md

@@ -1,12 +1,29 @@
 # Gemini Code Review Instructions
 
 - Do not comment on content for XML files or .matter content for clusters
-- Assume the matter specification is unknown and out of scope. Do not make uninformed assumptions about the Matter specification, or its contents.
-- Do not comment unless a change is probably desirable 
+- The SDK is implementing an in-progress matter specification that may not be available yet.
+  Assume the matter specification is unknown and out of scope. Do not make uninformed assumptions
+  about the Matter specification, or its contents.
+- Do not comment unless a change is probably desirable
 - Do not repeat yourself. Be concise without losing meaning
 - Do not over-explain what you see in the code. Only describe code if there are specific questions or concerns (or if a question is asked)
 - Ensure that extensions or fixes to existing code should match the prevailing style of the original code
 - Look for common typos and suggest fixes
-- The current year is 2025.
 - Wrong years and years in the future are OK. Humans will catch these issues.
-- Comments regarding issues about whitespace or code alignment are not needed. A code formatter will take care of these problems.
+- The SDK uses automated code formatting. Do not comment on whitespace, line length or other formatting
+  or whitespace issues. A code formatter will handle this.
+
+## Development guides
+
+The SDK source code contains guides for development best practices in `docs/guides`, `docs/testing` and other `docs` locations.
+Use these as a reference for finding common patterns and potential issues in new code. In particular:
+  - [docs/guides/writing_clusters](https://github.com/project-chip/connectedhomeip/blob/master/docs/guides/writing_clusters.md) describes how cluster handling
+    is to be implemented
+  - [docs/guides/migrating_ember_cluster_to_code_driven.md](https://github.com/project-chip/connectedhomeip/blob/master/docs/guides/migrating_ember_cluster_to_code_driven.md)
+    describes how ember clusters can be migrated to code driven
+  - [docs/testing/unit_testing.md](https://github.com/project-chip/connectedhomeip/blob/master/docs/testing/unit_testing.md)
+    describes how to implement unit testing
+  - [docs/testing/integration_tests.md](https://github.com/project-chip/connectedhomeip/blob/master/docs/testing/integration_tests.md)
+    describes how to implement integration tests.
+
+