Update pull_request_template.md

[categulario]

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

  It was useful to find the note about adding changes to the changelog. It might be as useful to ask people to run cargo fmt before making the pull-request

[michaelkirk]

Thanks!