Add a changelog section to the PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -17,3 +17,9 @@ If you believe the contents of any of these files need to be changed, please [op
 If the PR addresses an existing bug or feature, please reference it here.
 
 To help speed up the process and reduce the time to merge please ensure that `Allow edits by maintainers` is checked before submitting your PR. This will allow the project maintainers to make minor adjustments or improvements to the submitted PR, allow us to reduce the roundtrip time for merging your request.
+
+# Changelog
+
+Make sure that your pull request contains a changelog entry. You can run `make external-changelog` to create a placeholder entry. See [Changelog documents in CONTRIBUTING.md](aws/aws-sdk-go-v2/blob/main/CONTRIBUTING.md#changelog-documents) for more details.
+
+You can generate a UUID either by running `uuidgen` or by visiting a site like [uuidtools](https://www.uuidtools.com/v4)