Add demo at ember-pop-over.surge.sh

[kiwiupover]

Add demo url to which is used on emberaddons.com to display a demo link http://ember-pop-over.surge.sh

https://surge.sh/ is Static web publishing for Front-End Developers and it is free and easier than github pages.

Closes #13

[kiwiupover]

Actually to close #13 I will need to add the calendar component to the dummy app. I will do that later tonight.

[tim-evans]

Woo! Thanks for this

[tim-evans]

I'll let you figure some stuff out first. Coming up with a good docs site is hard. :/