Explain how to pass actions and then use actions that have been passed

[jenweber]

There are a few different ways to pass actions in Ember. We don't realllly teach them in the Guides, though it's covered in the Tutorial.

To do:

• link to this section on passing actions to components from here
• include a note that actions can't be passed down from a route, only from a controller or another component

Changes should only be made to the markdown files for the latest version of Ember.

[Parrryy]

I'd be happy to pick this up :)

[jenweber]

Closed by #177, thank you!