Update pull_request_template.md

Author: tabacitu

.github/pull_request_template.md

@@ -25,3 +25,11 @@
 ### How can we test the before & after?
 
 ??
+
+If the PR has changes in multiple repos please provide the command to checkout all branches, eg.:
+```bash
+git checkout "dev-branch-name" &&
+cd vendor/backpack/crud && git checkout crud-branch-name &&
+cd ../pro && git checkout pro-branch-name &&
+cd ../../..
+```