[Documentation] Add PR Template

[newtonick]

No description provided.

[kdmukai]

Random thoughts:

• Add something like a Background / Problem: basically what's the current state of things and why does it need to change?
• Describe the change.
• Explain any rationale if there's a deviation from the typical approach or if something was refactored.
• Within the testing section: If there are any new screens, add them to the screenshot generator or explain why they are omitted (e.g. too complicated, not yet possible in the screenshot generator). Include relevant screenshots in your PR description.
• Maybe also note other tips: "Try to keep your changes limited in scope; if you uncover other issues or improvements along the way, ideally submit those as a separate PR" (yes, I am the worst offender when it comes to PR scope creep...).

[jdlcdl]

This has my support.

[newtonick]

I'm merging this as is to start getting feedback so we can make more iterations if this proves to be helpful.