[Feature/neovim] generate docs if no doc directory is present

[mrcjkb]

For neovim plugins, check if a doc directory exists. If it doesn't, use something like panvimdoc to generate help files from the readme.

[mrcjkb]

NixOS/nixpkgs#321839 (comment)

[teto]

I feel like this should be its own action. I fear it's adding complexity when luarocks-tag-release is already complex and was not targeted for neovim but any lua package