correct metadata identation of "Example cross-project alerting rule" . 

https://docs.openshift.com/container-platform/4.18/observability/monitoring/managing-alerts/managing-alerts-as-a-developer.html#:~:text=Example%20cross%2Dproject%20alerting%20rule

Current : 

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: example-security
namespace: ns1 
spec:

Correct configuration should be:

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: example-security
  namespace: ns1        <------- correct identation
spec: