Readme.md: Use sudo to run docker exec.
Readme.md: Use sudo to run docker exec.

Signed-off-by: Gurucharan Shetty <a1872e333d0e52644f6125da2276530f7ebe5e77@ovn.org>

shettyg/ovn-docker,shettyg/ovn-docker,shettyg/ovn-docker