sdk: Add some usage documentation

This patch improves the README.md file adding some documentation about how to
use the SDK with Maven, and about the dependencies required.

Change-Id: Ic4b76369f4573465c6779e249664b104275e99e6
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>
(cherry picked from commit 25eddda411974849fbb3ea423298e085b1dd2ada)