Add "How to use this documentation" page

[mehalter]

Add a page describing "how to use this documentation" that talks about how all of the provided code snippets are lazy.nvim plugin(s) specifications that would be inside of the user's plugin configuration. Basically all configuration lives there.

Also if we want to make a section in AstroCommunity for having community entries for each documentation snippet it could have a way to find that given a page in the documentation? (this would take some discussion and design)

[mehalter]

I made a placeholder for this page on the v4 branch under using_the_docs.md in the root of the docs content (where the index.mdx file is)

[mehalter]

Done in latest commit