Documentation on custom actions

[Fryie]

The guides describe how to create custom helpers in the section on components, but they only give an example for a getter (query? or what's the appropriate lingo here?). However, they can also be used to create custom actions, see e.g. https://gist.github.com/migbar/3d961ddb7aaad1588949
A key step here (that wasn't clear to me from simply reading the Ceibo docs) is to use the buildSelector method, or you end up not getting your full selector (including scope and everything).

I think it would be nice if this was documented more thoroughly somewhere. :)