Merge pull request #1728: Update PR template

.github/pull_request_template.md

@@ -1,8 +1,8 @@
-### Description of proposed changes
+## Description of proposed changes
 
 <!-- What is the goal of this pull request? What does this pull request change? -->
 
-### Related issue(s)
+## Related issue(s)
 
 <!--
 Link any related issues here. Use GitHub's special keywords if appropriate¹.
@@ -11,7 +11,7 @@ Type `#` followed the name of an issue and GitHub will auto-suggest the issue nu
 ¹ https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/using-keywords-in-issues-and-pull-requests
 -->
 
-### Testing
+## Checklist
 
 <!--
 Make sure checks are successful at the bottom of the PR.
@@ -24,6 +24,7 @@ Please add a note if you need help with adding tests.
 -->
 
 - [ ] Checks pass
+- [ ] If making user-facing changes, add a message in [CHANGELOG.md](https://github.com/nextstrain/auspice/blob/HEAD/CHANGELOG.md) summarizing the changes in this PR
 - [ ] (to be done by a Nextstrain team member) [Create preview PRs on downstream repositories][1].
 
 [1]: https://github.com/nextstrain/auspice/blob/-/DEV_DOCS.md#test-on-downstream-repositories