fix cert-manager wrong path in standalone installation section (#2924)

Signed-off-by: mahdikhashan <[email protected]>

README.md

@@ -185,7 +185,7 @@ admission webhooks.
 Install cert-manager:
 
 ```sh
-kustomize build common/cert-manager/cert-manager/base | kubectl apply -f -
+kustomize build common/cert-manager/base | kubectl apply -f -
 kustomize build common/cert-manager/kubeflow-issuer/base | kubectl apply -f -
 echo "Waiting for cert-manager to be ready ..."
 kubectl wait --for=condition=ready pod -l 'app in (cert-manager,webhook)' --timeout=180s -n cert-manager