Update of README to add hack.courses
Update of README to add hack.courses

Update of README to add hack.courses as a project using xterm.js (https://hack.courses)
xtermjs/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js