Add better query docs.

[KonradStanski]

I've spent a few days trying to understand zoekt querying, and have come to the conclusion while its an amazing tool the docs suck.
I found this:
https://neogrok-demo-web.fly.dev/syntax
https://sourcegraph.com/docs/code-search/queries
https://sourcegraph.com/docs/code-search/queries/language
https://github.com/sourcegraph/zoekt/blob/main/doc

Theres also:
sourcegraph/zoekt#538

I'd like to go read the zoekt source code and maybe add some good docs and examples, and link to them from sourcebot.