Merge pull request #348 from kubukoz/nixpkgs

Update nix instructions

Author: romanowski

website/docs/_advanced_install.mdx

@@ -138,11 +138,9 @@ This method is provided and supported by the community, not the core team of Sca
 Scala CLI can be installed with [Nix](https://nixos.org) with
 
 ```bash
-nix-env -if https://github.com/kubukoz/scala-cli.nix/archive/refs/heads/main.tar.gz
+nix-env -if https://github.com/NixOS/nixpkgs/archive/refs/heads/master.tar.gz -A scala-cli
 ```
 
-or other methods listed in [the unofficial package's README](https://github.com/kubukoz/scala-cli.nix).
-
 </TabItem>
 
 </Tabs>
@@ -255,11 +253,9 @@ This method is provided and supported by the community, not the core team of Sca
 Scala CLI can be installed with [Nix](https://nixos.org) with
 
 ```bash
-nix-env -if https://github.com/kubukoz/scala-cli.nix/archive/refs/heads/main.tar.gz
+nix-env -if https://github.com/NixOS/nixpkgs/archive/refs/heads/master.tar.gz -A scala-cli
 ```
 
-or other methods listed in [the unofficial package's README](https://github.com/kubukoz/scala-cli.nix).
-
 </TabItem>
 </Tabs>