doc/neovim: better document the wrappers

[teto]

there is new wrapper interface wrapNeovimUnstable in development intended to be easier to use than the old wrapNeovim. It provides new fancy features that we would like to leverage/advertise
The interface is not definitive yet so we provide a translation layer to avoid breaking user configurations such that wrapNeovim still works. This explains why we document both at the moment with the goal to remove the old one once we ciment the interface.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[PerchunPak]

CC @BirdeeHub this is something you might be interested in

[BirdeeHub]

I kinda figured the wrapNeovimUnstable docs were kickstart-nix.nvim? I suppose that doesnt quite count as docs. I ate all the code from wrapNeovimUnstable for nixCats and changed it to fit nixCats so I know it well, due to editing almost every function. I labelled where its all from as well. But as you know, I am not good at docs XD

The above is kinda me joking but, yeah Im in favor of people knowing about these. Ups to teto for doing it.

But regardless, maybe inspiration can be pulled from there for documenting it.

[khaneliman]

Love the additional detail! Just finally read through it more and did some grammar corrections and consistency tweaks.

[teto]

@fricklerhandwerk i wanted to check the endresult by doing doc$ nix-build && firefox result/share/doc/nixpkgs/manual.html but clicking on the section led to 404.
Looking at the doc's doc (sic), I learned about the devmode command. Clicking http://127.0.0.1:8080/share/doc/nixpkgs/index.html#chap-language-support ends up with Cannot GET /share/doc/nixpkgs/index.html. Did I do something wrong ?

@khaneliman thanks for review. I've merged I think almost all of your comments. I think it's ready to go (we can squash from the UI).