Document files section of config for a target

[iislucas]

Would be great to document in the README the files section, and in particular note that src is within it, and also that files supports standard files descriptions and that all files in files are copied into the directory of the created chrome-app used for running the tests.

Might be good to give an example too... e.g... (this is from freedom-for-chrome)

jasmine_chromeapp: {
      providers: {
        files: [
          {src: 'freedom-for-chrome.js', dest: 'freedom-for-chrome.js'},
          {src: 'providers/**', dest: '/', cwd: freedomPrefix, expand: true},
          {src: 'spec/**', dest: '/', cwd: freedomPrefix, expand: true},
          {src: 'spec.js', dest: 'spec.js'},
        ],
        options: {
          paths: [
            'freedom-for-chrome.js',
            'spec.js'
          ],
          keepRunner: false
        }
      }
    }