docs: changes to broadcast documentation

- move BroadcastReceiver info to developer guide. see cl/140402421
- add usage note to CONNECTIVITY_ACTION broadcast

bug:32533262
bug:33106411

Change-Id: Ic2aa517831d29418e0c42aa6fc1e7f9aeb50f802
1 file changed
tree: cb8762ab3a2eb6bbde24d63786f7ccbf8571b79f
  1. core/
  2. services/
  3. tests/