Update .github/PULL_REQUEST_TEMPLATE.md

Co-authored-by: Olivier Halligon <olivier.halligon@automattic.com>

Author: rynaardb

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,4 +4,5 @@
 
 - [ ] Run `bundle exec rubocop` to test for code style violations and recommendations
 - [ ] Add Unit Tests (aka `specs/*_spec.rb`) if applicable
-- [ ] Run `bundle exec rspec` to run the whole test suite and ensure all your tests pass
+- [ ] Run `bundle exec rspec` to run the whole test suite and ensure all your tests pass
+- [ ] Make sure you added an entry in [the `CHANGELOG.md` file](https://github.com/wordpress-mobile/release-toolkit/blob/trunk/CHANGELOG.md#trunk) to describe your changes under the approprioate subsection.