docs: Request coarse location with b.g. location

When requesting background location access (for "all-the-time" access
to device location), it's possible to request *either* coarse or fine
location access along with background location access. Updated the
docs to mention this important point.

Test: make ds-docs -j32

Bug: 133248358
Change-Id: Ia10e493ecb33b6e971b53d3ff348a495417d9b38