Create PULL_REQUEST_TEMPLATE.md

[emisanada]

Create a Pull Request Template for issue #33

[SendGridDX]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[mbernier]

Hey, sorry about this #34 beat you to it!