Add workbench-example-app to home page

Added links to the workbench-example-app repo, as well as to live demos of the two example apps themselves. A plug-and-play way of getting started with scala-js-workebench without having to wallow in SBT trying to set it up correctly.
Merge pull request #26 from lihaoyi/patch-4

Add workbench-example-app to home page