Add some updates to documentation regarding concurrent camera operation.

- Add documentation about giving hints to camera HAL about concurrent
  operation before configuring sessions

- Limitations on ZOOM_RATIO_RANGE during concurrent operation.

Bug: 151891611

Test: builds

Change-Id: I79d0bd8be1ed9aa29a1ba080d01833f16eff580c
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>