Add it as a custom search engine in Chrome by entering chrome://settings/searchEngines in the search bar and clicking "add".
For the url just write javascript: and then paste the contents of toggle_gh.js after the colon, and hit save.
Alternatively, if you'd like a button, you can just paste the javascript: ... as a "new page" in bookmarks.
Like this:

I ended up changing the keyword to simply
tog