Create pull_request_template.md

[kkrug]

Created a template for new pull requests.

Description of changes

Link to issue

Issue Number:

Screenshots / Demo

Include steps a user would need to make in order to exercise the new functionality.

Checklist

• [ ] New functionality is tested and all tests are green
• [ ] If you have DB migration, it is a "safe" migration and you've confirmed it can be rolled back.
• [ ] If needed, README is up to date
• [ ] If applicable, Controllers modified contain appropriate authorization plugs

[r-bartlett-gsa]

@kkrug Can we add a few things to the template:

• PR is assigned to a project: Challenge_gov Board
• PR is assigned to a milestone: current sprint
• PR is assigned a reviewer, and requires code review and approval by a teammate