README.rst: fix link formatting

Make the links render correctly.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220803090250.136556-1-cohuck@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>