Fix target for Documentation link

[benji-york]

The target /doc/ is a 404. Instead, point to the top of the user section.

[benji-york]

The nav header works fine, the problem is with the footer.

[teto]

I kinda broke that link (the reason for the recent messy history) but it's tricky, the doc is served by another repo that downloads pages in /doc (https://github.com/neovim/doc/blob/main/ci/doc-index.sh) from this repo.
I renamed the doc folder to doc2/ to make it more obvious but it was a bad idea, it makes editing the pages a hassle.

I think we would like to have a working neovim.io/doc (easy to remember and pass on) that points towards the general doc rather than the generated :help (that's how it used to be until I messed it up).

To sum up I think we would want:

• rename doc2 back to doc
• use this layout

- title: Documentation
  url: /doc/
  sections:
    - title: General
      url: /doc/

which would require changes to https://github.com/neovim/doc/blob/main/ci/file-list.txt#L2

If this is too involving, I can understand, I have to fix it before the next release (1~2 weeks)

[teto]

cc @jamessan

[benji-york]

Thanks for the info, @teto. As you suspect, I don't think I have the bandwidth or context to fix this as you suggest — I was hoping this would be a quick fix. Feel free to close this PR.

If it would help, I'm happy to file an issue instead.

[justinmk]

would rather revert the doc/general/ thing and go back to having a single doc/ landing page. The content of doc/lsp/, doc/treesitter/, etc. does not justify separate landing pages.