add additional learning resource
add additional learning resource

Hey!

I created a screencast on ember-modal-dialog, and I thought linking to it in the documentation might be helpful to users who prefer to learn by watching rather than reading.
samselikoff/ember-modal-dialog,yapplabs/ember-modal-dialog,oscarni/ember-modal-dialog,yapplabs/ember-modal-dialog,mike-north/ember-modal-dialog,mike-north/ember-modal-dialog,samselikoff/ember-modal-dialog,oscarni/ember-modal-dialog