title: How to use --set to set values with Prometheus chart?
body: <p>For example, set <code>alertmanager.ingress.annotations</code> to add two items, both of these two methods not work:</p>
  
  <pre><code>$ helm install stable/prometheus \
    --set alertmanager.ingress.enabled=true \
    --set "alertmanager.ingress.annotations={alb.ingress.kubernetes.io/scheme: internet-facing, alb.ingress.kubernetes.io/tags: Environment=dev,Team=test}"
  
  Error: YAML parse error on prometheus/templates/alertmanager-ingress.yaml: error unmarshaling JSON: json: cannot unmarshal array into Go struct field .annotations of type map[string]string
  $ helm install stable/prometheus \
    --set alertmanager.ingress.enabled=true \
    --set "alertmanager.ingress.annotations={'alb.ingress.kubernetes.io/scheme': 'internet-facing', 'alb.ingress.kubernetes.io/tags': 'Environment=dev,Team=test'}"
  
  Error: YAML parse error on prometheus/templates/alertmanager-ingress.yaml: error unmarshaling JSON: json: cannot unmarshal array into Go struct field .annotations of type map[string]string
  </code></pre>
  
  <p>So how to use it?</p>