Neovim installation

There is now this. A config and highlights for tree-sitter-nu within nvim-treesitter.

Currently, - following installation/neovim.md - we override both, namely the config in plugin/init.lua and queries in queries/nu/*.scm.

plugin/init.lua also sets up filetype detection, which we might also be able to get upstreamed to neovim itself.

Then users would not have to install this repo as neovim plugin, see

{ "nushell/tree-sitter-nu", build = ":TSUpdate nu" },

in installation/neovim.md, probably saving users some diskspace but, more importantly, also supports installing nu support via just :TSInstall nu, without any additional line of configuration.

However, as it currently is, we have the advantage that we manage our queries/nu/*.scm ourselves. So we can easily make braking changes - i.e., renaming or removing nodes that queries refer to - because we directly control both, the grammar and the highlights. With a transition to the nvim-treesitter, we have to be careful whenever we do one of the two changes to our grammar, because we have to adjust queries in a different repo.

I hope that I made the situation clear to everyone who uses this parser in neovim.

Start with installation/neovim.md, then inspect plugin/init.lua and the queries/nu/*.scm files alongside the referenced nvim-treesitter commit. Determine which configuration and queries could move upstream and how grammar changes would be coordinated. Done means the integration plan is resolved and the affected installation or upstream changes are documented.