Create new script on Tampermonkey's dashboard and copy the UserScript header to the new .js file. Be sure to change <PATH> for the cloned directory's path.
// ==UserScript==
// @name Script Name
// @namespace http://tampermonkey.net/
// @version Version
// @description Description
// @author Author
// @match Site
// @icon Icon
// @require file://<PATH>/filename.js
// @require https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js // If it needs JQuery
// @grant GM_* // If it needs a Greasemonkey GM_* function
// ==/UserScript==- JQuery: While editing on Tampermonkey, it would complain
$didn't exist, so you had to add/* globals $ */after the UserScript header to remove the warning.
In Google Chrome, you can allow Tampermonkey to load scripts from the filesystem, by setting "Allow scripts to access local files" in Tampermonkey's settings. This is not allowed in Mozilla Firefox, so you have to copy the scripts' code into the browser.
In the case of library code, like Mutation Handler, you are forced to copy the code into the userscript.
Tampermonkey is a donationware userscript manager that is available as a browser extension. This software enables the user to add and use userscripts, which are JavaScript programs that can be used to modify web pages. Created by Jan Biniok (2010).