add non-schedulable pods alert - closes #115

Signed-off-by: Marcin Fabrykowski <git@fabrykowski.pl>

chart/templates/alerts/pods.yml

+apiVersion: monitoring.coreos.com/v1
+kind: PrometheusRule
+metadata:
+  name: prometheus-rules-pods
+  namespace: prometheus-system
+  labels:
+    prometheus: example
+    role: alert-rules
+spec:
+  groups:
+  - name: ./pods.rules
+    rules:
+    - alert: non schedulable pods
+      expr: kube_pod_status_phase{phase!="Running",phase!="Succeeded"} >0