Fix links and add note on issues
Fix links and add note on issues

Add Stack Overflow link

mroderick/Sinon.JS,fatso83/Sinon.JS,cjohansen/Sinon.JS,mroderick/Sinon.JS,cjohansen/Sinon.JS,mroderick/Sinon.JS,fatso83/Sinon.JS,fatso83/Sinon.JS,cjohansen/Sinon.JS