Drop this file in your wp-content/mu-plugin folder if you want to fire and forget or just into your wp-content/plugins folder if you want to be able to activate.
Now that WordPress 5.0+ has the new block editor merged in, the Gutenberg plugin is for development of features that are not in WordPress core. Since I contribute to the plugin among other projects I do I find that sometimes I forget whether or not the GB plugin is active or not. So I created this handy snippet that inserts a GB is Active indicator in the WordPress admin bar menu when the plugin is active.