Add .local.fish for machine-local settings

nix/modules/fish/default.nix

@@ -65,6 +65,10 @@ let tide_conf = builtins.readFile ./tide_config.fish; in
         source "$HOME/.cargo/env.fish"
       end
 
+      if test -f $HOME/.local.fish
+        source $HOME/.local.fish
+      end
+
       ${builtins.readFile ./tide_config.fish}
       '';