Expand PR template with reminder to update CHANGELOG.md

.github/pull_request_template.md

@@ -4,6 +4,8 @@ Please read the "Making a PR" section of [`CONTRIBUTING.md`](https://github.com/
 * Keep your PR:s small and focused
 * If applicable, add a screenshot or gif
 * Open the PR as a draft until you have self-reviewed it and it is green
+* If it is a noteworthy change, add a line to the relevant `CHANGELOG.md`
+* When you have addressed a PR comment, mark it as resolved
 -->
 
 Closes <https://github.com/emilk/egui/issues/THE_RELEVANT_ISSUE>.