[Docs] GitHub Pull Request guidelines

[JSKitty]

To bring order in the midst of our chaos, we now have a neat little template for each PR devs submit, and here's a few reasons it's neat:

• It's standardised: we can all use a familiar, digestible format.
• Devs get a breakdown: allowing them to dig in to add/improve the PR without guess-work.
• Reviewers get a high-level overview: so they know the functionality to expect, and can test + verify.
• Easier for our LMP team to 'convert' each PR in to a Proposal: making it easier for devs to be rewarded.

GitHub will automatically display this template for all future PRs post this one's merge, so no copy/pasting required, just filling a few areas and pushing.

[Liquid369]

ACK

I do not see a reason for any changes to this template currently as we will learn what the DAO will like more to assist our proposals

[Duddino]

ACK