[github] Switch from the old Jira format to github issues for the PR template

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 bugs in the Swift bug tracker, provide a link: -->
-Resolves SR-NNNN.
+<!-- If this pull request resolves any issues in the Swift github, mention it: -->
+Resolves #NNNNN.
 
 <!--
 Before merging this pull request, you must run the Swift continuous integration tests.