Updated deployment to mention pm2

I have just very recently discovered https://github.com/Unitech/PM2/ and now after using it for a bit it seems quite a bit superior to me than forever, especially with things like https://github.com/Unitech/pm2#deployment or 0s downtime deployment.
So I think it should be mentioned as an alternative to forever.

Also I have added a line just to mention where the production config is stored.