Update pull_request_template.md

[riotschoolacc]

Changes

Updated the template for pull requests to be more helpful and user-friendly.

Checks

Put an X in the brackets to checkmark them. (This is new!)
By submitting your pull request for review, you agree to the following:

• This pull request was created in whole or in part by me, and I have the right to submit it under the terms of this repository's open source licenses.
• I understand and agree that this contribution and a record of it are public, maintained indefinitely, and may be redistributed under the terms of this repository's open source licenses.
• To the best of my knowledge, all proposed changes are accurate, and do not contain any content that can be considered harmful or inappropriate. (This was changed to add more content.)