docs: add information about nvfetcher

CONTRIBUTING.md

@@ -7,10 +7,16 @@ Create a file in `modules/<module>/` with the name of the port. Add the file to
 `catppuccin.enable` and `catppuccin.flavour` options, and optionally the
 `catppuccin.accent` option. `catppuccin.flavour` and `catppuccin.accent` should
 default to `config.catppuccin.flavour` and `config.catppuccin.accent`, respectively.
-[Flake inputs](https://nixos.wiki/wiki/Flakes#Input_schema) should also be used over
-`fetchFromGitHub` when themes are not avalible in nixpkgs - this in order to reduce
-[IFD](https://nixos.wiki/wiki/Import_From_Derivation) and allow for auto-updating the 
-specified commits for repositories.
+
+[nvfetcher](https://github.com/berberman/nvfetcher) is used to track our upstream
+sources to use in modules. This allows us to reduce [IFD](https://nixos.wiki/wiki/Import_From_Derivation)
+and auto-update all themes. Most repositories can be specified like so:
+
+```toml
+[program_name]
+src.git = "https://github.com/catppuccin/program_name.git"
+fetch.github = "catppuccin/program_name"
+```
 
 After creating your module, add the options to enable it in `test.nix` under the
 `nodes.machine` attrset. This will allow for your configuration to be tested along