Docs: update pull request page

[agjohnson]

From #9258

• the content looks good, it could use a more marketing language to sell it more, but it's fine for now
• maybe some small edits will help

[cletheren]

Hello, I am a newcomer to the project and I'd like to see whether I can assist with this issue. For the avoidance of any doubt (and to help me as a newcomer), would you mind pointing me to the page that you're referring to please?

[agjohnson]

The documentation page discussed here is https://docs.readthedocs.io/en/stable/pull-requests.html

[humitos]

I understand this page was reviewed when we added addons documentation here. The work mentioned in the description looks outdated and/or done already.