Install shell completions

pkgs/tools/misc/tmuxinator/default.nix

@@ -1,4 +1,4 @@
-{ lib, buildRubyGem, ruby }:
+{ lib, buildRubyGem, ruby, installShellFiles }:
 
 # Cannot use bundleEnv because bundleEnv create stub with
 # BUNDLE_FROZEN='1' environment variable set, which broke everything
@@ -37,6 +37,12 @@ buildRubyGem rec {
 
   propagatedBuildInputs = [ erubis thor xdg ];
 
+  nativeBuildInputs = [ installShellFiles ];
+
+  postInstall = ''
+    installShellCompletion $GEM_HOME/gems/${gemName}-${version}/completion/tmuxinator.{bash,zsh,fish}
+  '';
+
   meta = with lib; {
     description = "Manage complex tmux sessions easily";
     homepage    = "https://github.com/tmuxinator/tmuxinator";