stackdriver: improve config page info box documentation

public/app/plugins/datasource/stackdriver/partials/config.html

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 <div class="gf-form-group">
   <div class="grafana-info-box">
   <div class="grafana-info-box">
-    <h5>GCP Service Account</h5>
+    <h4>Stackdriver Authentication</h4>
+    <p>There are two ways to authenticate the Stackdriver plugin - either by uploading a Google JWT file, or by
+      automatically retrieving credentials from Google metadata server. The latter option is only available
+      when running Grafana on GCE virtual machine.</p>
+
+    <h5>Uploading a JWT file</h5>
     <p>
     <p>
-      To authenticate with the Stackdriver API, you need to create a Google Cloud Platform (GCP) Service Account for
+      First you need to create a Google Cloud Platform (GCP) Service Account for
       the Project you want to show data for. A Grafana datasource integrates with one GCP Project. If you want to
       the Project you want to show data for. A Grafana datasource integrates with one GCP Project. If you want to
       visualize data from multiple GCP Projects then you need to create one datasource per GCP Project.
       visualize data from multiple GCP Projects then you need to create one datasource per GCP Project.
     </p>
     </p>
     <p>
     <p>
-      The <strong>Monitoring Viewer</strong> role provides all the permissions that Grafana needs.
+      The <strong>Monitoring Viewer</strong> role provides all the permissions that Grafana needs. The following API
+      needs to be enabled on GCP for the datasource to work: <a class="external-link" target="_blank" href="https://console.cloud.google.com/apis/library/monitoring.googleapis.com">Monitoring
+        API</a>
     </p>
     </p>
+
+    <h5>GCE Default Service Account</h5>
     <p>
     <p>
-      The following APIs need to be enabled on GCP for the datasource to work:
-      <ul>
-        <li><a class="external-link" target="_blank" href="https://console.cloud.google.com/apis/library/monitoring.googleapis.com">Monitoring
-            API</a></li>
-        <li><a class="external-link" target="_blank" href="https://console.cloud.google.com/apis/library/cloudresourcemanager.googleapis.com">Resource
-            Manager API</a></li>
-      </ul>
+      If Grafana is running on a Google Compute Engine (GCE) virtual machine, it is possible for Grafana to
+      automatically retrieve default project id and authentication token from the metadata server. In order for this to
+      work, you need to make sure that you have a service account that is setup as default account for the virtual
+      machine and that the service account has been given read access to the Stackdriver Monitoring API.
     </p>
     </p>
+
     <p>Detailed instructions on how to create a Service Account can be found <a class="external-link" target="_blank"
     <p>Detailed instructions on how to create a Service Account can be found <a class="external-link" target="_blank"
         href="http://docs.grafana.org/datasources/stackdriver/">in
         href="http://docs.grafana.org/datasources/stackdriver/">in
-        the documentation.</a></p>
+        the documentation.</a>
+    </p>
   </div>
   </div>
 </div>
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