chore(docs) Small fixes in language guide and mode reference

[edemaine]

I found a couple of small typos, and references to the old className, while reading the docs, so thought I'd push them along here.

Changes

• Change className to scope, "name" to "scope"
• Add link to Scopes Reference from Language Guide too (copied from Mode Reference). I don't know how to render reStructuredText so I assume this link renders OK but haven't verified.
• Fix typo "many" to "must"

Checklist

• Added markup tests, or they don't apply here because just changing documentation
• Updated the changelog at CHANGES.md

[joshgoebel]

This would need to be rebased on #3159 where I think I've already got most of this... it's just not in main yet.

[joshgoebel]

@edemaine Any chance you'd like to possibly help out by doing some more reviewing of PRs? That's the big road block right now to forward momentum. If you'd like to help out there find me on Discord.

[edemaine]

I tried rebasing onto #3159, and these changes seem to still be relevant (no conflicts).

[joshgoebel]

Oh... maybe it's another PR then... we'll leave this be then until everything merges and then have a fresh look.

[joshgoebel]

You were right, guess I missed these. Thanks so much!