add md extension, add readme for changelogs

changelogs/README.md

@@ -0,0 +1,14 @@
+## Adding a changelog
+
+Pull request authors are expected to include a changelog file explaining the changes introduced by the pull request. 
+The changelog file should be a new file created in the `changelogs/unreleased` folder. 
+The file should follow the naming convention of `pr-username` and the contents of the file 
+should be your text for the changelog.
+
+### Example
+```
+changelogs/unreleased   # folder to place changelogs
+    101-username        # your changelog file (pull request #101 by @username)
+```
+
+If a pull request does not warrant a changelog, the CI check for a changelog can be skipped by applying a `changelog-not-required` label.