Add some options and instructions to have virgl support from inside a container
This add some options that will be useful when running virgl from inside a container with the vtest server running on the host.
- use-pid-ns - If we want to share the container ns at some point
- ready-fd - Needed to wait for the server to be ready before starting the container. It is used by the OCI hooks
There is also some instructions and scripts to help to build and run a container with virgl support.