Update PULL_REQUEST_TEMPLATE.md

Author: finagolfin

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,8 +1,8 @@
 <!-- What's in this pull request? -->
 Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.
 
-<!-- If this pull request resolves any issues in the Swift github, mention it: -->
-Resolves #NNNNN.
+<!-- If this pull request resolves any issues in the Swift github, mention them: -->
+Resolves #NNNNN, fix apple/llvm-project#MMMMM.
 
 <!--
 Before merging this pull request, you must run the Swift continuous integration tests.