github-issue-branch-name.user.js

// ==UserScript==
// @name         Github Issue Branch Name
// @namespace    http://agate.github.com
// @version      0.1
// @description  Auto generate feature branch with issue's title
// @author       agate
// @match        https://github.com/*/*/issues/*
// @grant        none
// ==/UserScript==

var $jqTitle = $('.gh-header-title');
var title = $jqTitle.text();
var branchName = title.split("\n").join(" ")
                      .replace(/\s+/g, " ").trim().toLowerCase()
                      .replace(/[^\w ]/g, ' ')
                      .replace(/\s+/g, '_')
                      .replace(/^_*/, '');

$jqTitle.append('<span style="display: block; color: gray; font-size: 18px; font-weight: lighter; margin-top: 8px;"><strong>BRANCH NAME:</strong> ' + branchName + '</span>');