cleanup readme installation instructions (#380)
cleanup readme installation instructions (#380)

Signed-off-by: Craig Tabita <c95209339fb69a84d35cb824f5e808bb6159a41e@google.com>
open-policy-agent/gatekeeper,open-policy-agent/gatekeeper,open-policy-agent/gatekeeper,open-policy-agent/gatekeeper,open-policy-agent/gatekeeper