docs(readme): Add singleRun option in Grunt Watch Session

Specifying the `singleRun: false` option in Grunt Watch Session to ensure people get the example working even if the karma config file specify `singleRun: true`. With singleRun set to true, the example will fail because the server is stopped after each test run.

Closes #49, #114
Merge pull request #114 from oliamb/master

Add singleRun option in Grunt Watch Session