tc docker: Updated setup.sh buildscript

The change in setup.sh includes:
 * setup the environment to build TC images
 * setup.sh now also builds a Docker image
 * README.md update for the usage

Signed-off-by: Rupinderjit Singh <rupinderjit.singh@arm.com>
Change-Id: I8ef3ed20d56e94c9cc9b1d71c36e14f36415260c