Remove DOCKER-VERSION, easier to maintain
Add example of multiple FROM steps
Upstream-commit: 9416574569b3969f1844c83cf4e24bc50957aaf5
Component: engine
Standardizes on uppercase for instructions, gives
example usage.
Wrap at 80 columns
Upstream-commit: a98eafaf58ea250d6cd75d2f175f66d705d4a0eb
Component: engine