docs: link to org-wide Contributor Guide

Author: alpha912

CONTRIBUTING.md

@@ -3,3 +3,5 @@
 - Use DCO sign-off on commits: `git commit -s -m "..."`.
 - Open issues and PRs. Small, focused changes preferred.
 - See governance: https://github.com/bharataddress/governance
+
+Contributor Guide: https://github.com/BharatAddress/.github/blob/main/AGENTS.md

README.md

@@ -43,3 +43,7 @@ Docker:
 docker build -t ghcr.io/bharataddress/api-server:dev .
 docker run -p 8000:8000 ghcr.io/bharataddress/api-server:dev
 ```
+
+## Contributor Guide
+
+- Central guidelines: https://github.com/BharatAddress/.github/blob/main/AGENTS.md