[clojure-deps-edn] Create Pull Request template to guide contributions

[practicalli-johnny]

Please raise an issue before raising a pull request in order to avoid working on something that would not be accepted.

Sweeping changes to this repository (or any open source project) are less likely to be accepted and take longer to review and test by the maintainers.

For example, updating a number of different libraries all at once will require a lot of manual testing to ensure each alias still works, especially with some of the recent changes in the ClojureScript library.

Pull requests that change deprecated aliases will be rejected. Those aliases are to be removed, so no further testing will be done. Updating deprecated aliases does not demonstrate an understanding of the project concerns.