Add redirect for PRs to appropriate GitHub repo

Author: evankanderson

.github/pull_request_template.md

@@ -0,0 +1,20 @@
+# Repo Move!!
+
+Hello contributor!  This repo is being migrated into https://github.com/cncf/toc and https://github.com/cncf/contribute-site.  If you're thinking of opening a PR here, you should probably open it over there instead.
+
+## Mappings
+
+* If you're editing `community/assessments/projects` for a self-assessment or joint assessessment, your new location is:
+
+  https://github.com/cncf/toc/tree/main/projects/<yourproject>/security-assessment/...
+
+* If you're updating published resources in `community` outside the assessments, your new location is:
+
+  https://github.com/cncf/contribute-site/tree/main/docs/community/tags/security-and-compliance
+
+* If you're editing other content, it probably should go to:
+
+  https://github.com/cncf/toc/tree/main/tags/tag-security-and-compliance/
+
+
+Thanks!