[DOC] Update the guidelines on linked issues/PRs

[mberz]

The mention of "closes #issue number" is not always reliable in cases where the specific formatting is not matched.
We should add a sentence on using the "development" section in the right hand menu bar to properly link issues and pull requests.

[MrIridescent]

Hi! I'd like to take a look at this. I'm new to the project but I've fixed similar issues before. I'll submit a PR shortly.