Update `README.md` with information for use of the container

[gbraad]

Since a recent change 97c7658 a Dockerfile has been introduced

vmproxy/Dockerfile

Lines 10 to 13 in 97c7658

	FROM scratch
	COPY --from=builder /go/bin/vmproxy /go/bin/vmproxy
	COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
	ENTRYPOINT ["/go/bin/vmproxy"]

Perhaps a good idea to add information regarding the docker/podman build and use of this container, such as:

$ [docker|podman] run --name vmproxy -d --env TS_AUTHKEY="" ghcr.io/shayne/vmproxy:latest <vmname> <vnc portaddr>

Note: I believe more changes are needed, as

vmproxy/cmd/vmproxy/main.go

Line 22 in 97c7658

libvirtLoc = flag.String("libvirt-loc", "/var/run/libvirt/libvirt-sock", "libvirt socket path or <ip addr>:<port>")

was added to allow the container to communicate with the libvirt.sock ;-)