Reorganization of best practices and addition of overlays for globals

[baywet]

fixes #200
This does a couple of things:

• Makes the best practices into a section
• Moves the topics under best practices to dedicated pages (verbatim, no changes were made besides links)
• Adds a new best practice to use overlays for globals

Heavy use of GH Copilot to help with the reorganization and the wording

[lornajane]

I love this! And sorry, I added loads of comments, should I have just edited? I know half of this isn't yours. The Overlays for global updates is great!

[baywet]

@lornajane thanks for the review. I have "moved" the feedback on existing content to #203. I don't think we should address it here since:

• it was already published
• it'll make the review process lengthier
• it's a verbatim move of the existing content, I didn't change anything (other than adding the overlay one)

Let me know if you still have suggestions on the overlay article, otherwise we should be good to merge as is and follow up with another PR to address the concerns you had on existing content.

[lornajane]

This makes sense. Let's work on the restructure so we've got somewhere to land this article!

[baywet]

@lornajane let me know if you have any additional feedback specific to this new article. Otherwise it's ready for another review.