PULL_REQUEST_TEMPLATE.md

Thanks for starting a pull request on Material Components!

Don't forget:

• Identify the component the PR relates to in brackets in the title. [Buttons] Updated documentation
• Link to GitHub issues it solves. closes #1234
• Please add unit tests, snapshot tests, or manual testing steps depending on the change.
• Sign the CLA bot. You can do this once the pull request is opened.

Contributing has more information and tips for a great pull request.