Add viewcount to readme

I thought this might be interesting as an experiment to get the 3 (that I'm aware of so far) browserify middleware repos on viewcount.

Once it has at least one view you can see how many views it has by going to https://viewcount.jepso.com/shtylman/node-enchilada

_Disclaimer:_ I run viewcount and put mine on there a few hours ago, so have about a 50 view head start.

P.S. If you login at https://viewcount.jepso.com/ then it won't count your own views.