Fixed the missing '-r' in the Flask install instructions.
Fixed the missing '-r' in the Flask install instructions.

worldline-spain/openxc-vehicle-simulator,iamthebest77/openx,worldline-spain/openxc-vehicle-simulator,NitishKSharma/openxc-vehicle-simulator,NitishKSharma/openxc-vehicle-simulator,worldline-spain/openxc-vehicle-simulator,dhootha/openxc-vehicle-simulator,openxc/openxc-vehicle-simulator,apiri/openxc-vehicle-simulator,iamthebest77/openx,openxc/openxc-vehicle-simulator,NitishKSharma/openxc-vehicle-simulator,dhootha/openxc-vehicle-simulator,apiri/openxc-vehicle-simulator,dhootha/openxc-vehicle-simulator,iamthebest77/openx,openxc/openxc-vehicle-simulator,apiri/openxc-vehicle-simulator