Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
// Add link to Navigation portlet
$(mw.loader.using(['mediawiki.util', 'mediawiki.Title'], () => {
	mw.util.addPortletLink(
		'p-navigation',
		new mw.Title('Wikipedia:WikiProject Guild of Copy Editors').getUrl(),
		'Guild of Copy Editors',
		'n-guild',
		'The Guild of Copy editors',
		null
	);
}).catch(console.error));