[REQUEST] Improve :doc searchability

[Supreeeme]

Feature

Kakoune's built in docs are helpful, however I find they are not particularly discoverable if you don't actually know what category to search for.
For example, in setting up kakoune-lsp, you add this line to your config:

eval %sh{kak-lsp}

Seeing this for the first time, I was curious how %shworks. Doing a :doc sh or :doc %sh gives me nothing. Doing :doc eval takes me to doc-execeval which makes no mention of %sh. I had to actually peruse random docs to discover it's described under :doc expansions, which was really unclear to me. I imagine myself and others new to Kakoune will end up running into more things like that. I think it would be useful if at least one of two things could happen here:

• Allow searching through all docs, similar to vim's :helpgrep. Maybe :docgrep?
• Increase the number of things considered as "topics" for :doc

I think both of these would be useful, but I imagine something like :docgrep would be easier to immediately implement.

Usecase

No response

[Supreeeme]

Immediately after writing this issue I discovered :doc expansions sh will jump right to the %sh section of the expansions doc. This still requires you to know the docs for %sh live in the docs for expansions, but maybe this can be leveraged somehow?