add external-service shared notebook example

examples/service-notebook/external/jupyterhub_config.py

@@ -0,0 +1,24 @@
+# our user list
+c.Authenticator.whitelist = [
+    'minrk',
+    'ellisonbg',
+    'willingc',
+]
+
+# ellisonbg and willingc have access to a shared server:
+
+c.JupyterHub.load_groups = {
+    'shared': [
+        'ellisonbg',
+        'willingc',
+    ]
+}
+
+# start the notebook server as a service
+c.JupyterHub.services = [
+    {
+        'name': 'shared-notebook',
+        'url': 'http://127.0.0.1:9999',
+        'api_token': 'super-secret',
+    }
+]