* PR Template: Flip order of checklist and details
Because:
If the details are first, they are viewable in Discord's webhook.
This PR:
* Moves the detail sections to the beginning of the template
* Moves the checklist section to the end of the template
* Adds an issue section to link the issue
* Adds the Because, This PR, and Issue sections to checklist
* Reduce wording that is not essential
