Update pull_request_template.md

Author: kingthorin

.github/pull_request_template.md

@@ -1 +1,4 @@
 :warning: Have you followed the [contributions guideance](https://owasp.org/www-project-web-security-testing-guide/#contributions)? Content PRs should generally be made against the the [source repo `OWASP/wstg`](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.