Added Docker usage warning
Added Docker usage warning

Note in response to @tylermzeller running into issues running both Docker
and an Android emulator.

jihunhamm/Crowd-ML,jihunhamm/Crowd-ML,jihunhamm/Crowd-ML,jihunhamm/Crowd-ML,jihunhamm/Crowd-ML,jihunhamm/Crowd-ML,jihunhamm/Crowd-ML