feat: add shell completion generation

flake.nix

@@ -65,6 +65,10 @@
             src = ./.;
             vendorHash = "sha256-EpGgfiCqJjHEOphV2x8FmXeIFls7eq2NVxb/or4NLUo=";
 
+            nativeBuildInputs = with pkgs; [
+              installShellFiles
+            ];
+
             subPackages = [
               "."
             ];
@@ -75,6 +79,13 @@
               sed -i "s/rm -rf SpotiFLAC//g" ./tools/fetch_spotiflac_backend.sh
               ./tools/fetch_spotiflac_backend.sh
             '';
+
+            postInstall = ''
+              installShellCompletion --cmd spotiflac-cli \
+                --bash <($out/bin/spotiflac-cli completion bash) \
+                --fish <($out/bin/spotiflac-cli completion fish) \
+                --zsh <($out/bin/spotiflac-cli completion zsh) 
+            '';
           });
         }
       );

main.go

@@ -17,6 +17,7 @@ func main() {
 
 	cmd := &cli.Command{
 		Name: "spotiflac-cli",
+		EnableShellCompletion: true,
 		Flags: []cli.Flag{
 			&cli.StringFlag{
 				Name:        "download",