Update README.md with some initial info
Update README.md with some initial info

Fill in background, getting started, license information, etc.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>
mkhon/tcmu-runner,open-iscsi/tcmu-runner,agrover/tcmu-runner,rancher/tcmu-runner,lxbsz/tcmu-runner,yasker/tcmu-runner,superlibj/tcmu-runner,open-iscsi/tcmu-runner,liuy/tcmu-runner,JefferyHu/tcmu-runner