Add docs for jscoverage + mocha

[beaugunderson]

I'm using covershot successfully with mocha and TJ's version of node-jscoverage with this simple script.

I did require my fix for printing source lines in #9 before I got source in the HTML report.

Would be great to get that into the docs so people aren't scared off by having to rewrite all the require()s in their tests. :)