Add ignore specific files example. Closes GH-82.
Add ignore specific files example. Closes GH-82.

- Documentation now has an example of using the ignores option
- Also explains what happens if a file is in files array and is
  ignored -- the file is ignored

christian-bromann/grunt-contrib-jshint,djchie/grunt-contrib-jshint,marionm/grunt-contrib-jshint,jl9n/grunt-contrib-jshint,thomasboyt/grunt-jsxhint,gruntjs/grunt-contrib-jshint