Add line about socket.io in readme.
Add line about socket.io in readme.

ciberch/node-express-boilerplate,ciberch/node-activities-boilerplate,mape/node-express-boilerplate,dongguangming/node-express-boilerplate,toantran/scrumtrak,praveenjha527/node-express-boilerplate,nickjenkin/moody-chef