Update CONTRIBUTING.rst

[Warchamp7]

Description

Updates the Contributing Guidelines with the guidelines proposed by @PatTheMav in https://github.com/obsproject/obs-studio/pull/11622

Motivation and Context

Document these desired changes to code.

How Has This Been Tested?

N/A

Types of changes

• Documentation (a change to documentation pages)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.