Add contribution advice to docs about PRs

[h1divp]

For newer members who join this project, adding some advice for what to include in PRs (like saying "this PR fixes issues #0000") and other general points for what a comment should have could be added. Referring people to this page/section before contributing could potentially make future PRs have a lot more quality. I would add things like:

• Note what issue your PR fixes in the description
• Describe your changes, what has been tested (hopefully all new changes), what might need testing, etc
• How to make a good title (also would go for commits)

I know some older folks who have given good advice about what PRs and issues should contain. I think it should certainly be relayed to newer folk who are getting their feet wet with contributing to a project. If you have good advice in this area please shoot me a DM on discord.

[AlexanderWangY]

I gotchu phoenix