sidebar.user.js

// ==UserScript==
// @name         Charcoal Team Sidebar Link
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Re-adds a link to the Charcoal team to the sidebar
// @author       You
// @match        https://stackoverflow.com/
// @icon         https://www.google.com/s2/favicons?sz=64&domain=stackoverflow.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var a = document.createElement("a");
    a.href = "https://stackoverflowteams.com/c/charcoal/questions";
    a.innerText = "Charcoal Team";
    document.getElementsByClassName("js-create-team-cta")[1].appendChild(a);
})();