Update index.md

Author: kingthorin

index.md

@@ -20,6 +20,9 @@ The WSTG is a comprehensive guide to testing the security of web applications an
 
 Any contributions to the guide itself should be made via the [guide's project repo](https://github.com/OWASP/wstg).
 
+> [!CAUTION]
+> Contributions should only be made in the proper repo against the latest content. Please don't open PRs here for versioned or stable content, they represent point-in-time state.  
+
 ## Stable
 
 View the always-current stable version at [stable](stable/).