Add docs

[clason]

Separate docs repo with manuals:

• writing grammars (workflow, intro, advanced topics from amaanq)
• writing queries (intro, tools, tutorials?)
• ...?

Include content from https://github.com/sogaiu/ts-questions (with permission). (Current upstream docs are not great for queries: spread over two pages and mix in crate config. Seems easier to start from scratch.)

[ObserverOfTime]

Do we need a separate repo? They could be in this repo in a docs folder (or the wiki).

[clason]

For visibility (and possible deployment), I would say so, yes. (I envision this to be a growing effort.)

Doesn't mean we can't start smaller, of course.