docs($compile): usage of bindToController as object is undocumented

[gjungb]

Since version 1.4 it's possible to use bindToController as an object like so:

bindToController: {
  text: '@text',
  obj: '=obj',
  expr: '&expr'
},
scope: {}

This fact is not reflected in the documentation.

[Narretz]

Yeah, that's right! Would you like to submit a PR that adds the info?

[Nazanin1369]

@Narretz Putting up a PR today for this