libretro: update README.md

pkgs/applications/emulators/retroarch/README.md

@@ -1,46 +1,16 @@
-# RetroArch
+# Libretro
 
-This directory includes [RetroArch](https://www.retroarch.com/), [libretro
-cores](https://docs.libretro.com/guides/core-list/) and related packages.
+[libretro cores](https://docs.libretro.com/guides/core-list/) and related
+packages.
 
 ## Adding new cores
 
 The basic steps to add a new core are:
 
-1. Add the core repository to [update_cores.py](./update_cores.py) inside the
-   `CORES` map.
-   - The minimum required parameter is `repo`
-   - If the repository owner is not `libretro`, set `owner` parameter
-   - If the core needs submodules, set `fetch_submodules` parameter to `True`
-   - To pin the core to a specific release, set `rev` parameter
-2. Run `./pkgs/applications/emulators/retroarch/update_cores.py <emulator>` to
-   generate [`hashes.json`](./hashes.json) file
-3. Add your new core to [`cores.nix`](./cores.nix) file, using
-   [`mkLibretroCore`](./mkLibretroCore.nix) function
-   - In general, the attribute name should be the same as the repo name, unless
-   there is a good reason not to
-   - Check the core repo and [Libretro
-   documentation](https://docs.libretro.com/) for the core you're trying to add
-   for instructions on how to build
-   - Also check the examples inside [`cores.nix`](./cores.nix)
-   - If your core is recently released, there is a good chance that you may
-   need to update [`libretro-core-info`](./libretro-core-info.nix) for things
-   to work inside RetroArch
-4. Try to build your core with `nix-build -A libretro.<core>`
-
-## Updating cores
-
-Just run:
-
-```console
-# From the root of your nixpkgs directory
-./pkgs/applications/emulators/retroarch/update_cores.nix
-```
-
-Keep in mind that because of the huge amount of cores that we package here, it
-is recommended to set `GITHUB_TOKEN` to your GitHub's [Personal Access
-Token](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens)
-(PAT), otherwise the update will probably fail due to GitHub's API rate limit.
+1. Add a new core using `mkLibretroCore` function (use one of the existing
+   files as an example)
+2. Add your new core to [`default.nix`](./default.nix) file
+3. Try to build your core with `nix-build -A libretro.<core>`
 
 ## Using RetroArch with cores