Update README.md
allowed cli usage with existing mgmt server by allowing the 'use' command without a prior 'init' call
Merge remote-tracking branch 'origin/feature/CLOUDIFY-2440-Allow-providerless-init' into feature/CLOUDIFY-2440-Allow-providerless-init
Merge pull request #17 from CloudifySource/feature/CLOUDIFY-2440-Allow-providerless-init

allow using CLI with an existing management server