Handle the hardcoded configuration values

This patch allows to customize the hardcoded configuration values,
as well as introduce new configuration options for aodh services
by configmap template with the specified section:

  aodh:
    server:
      configmap:
        DEFAULT:
          rest_notifier_max_retries: 0
          notifier_topic: alarming
        api:
          user_alarm_quota: 10
          project_alarm_quota: 10
          alarm_max_actions: -1

Change-Id: I49fe8402d99b1cefb58e3449137df255924d3f2b
Related-Prod: PROD-29627
diff --git a/README.rst b/README.rst
index 624468c..04e79ed 100644
--- a/README.rst
+++ b/README.rst
@@ -162,6 +162,22 @@
                 - host: 127.0.1.1
                 - host: 127.0.2.1
 
+Change default options using configmap template settings
+========================================================
+
+.. code-block:: yaml
+
+    aodh:
+      server:
+        configmap:
+          DEFAULT:
+            rest_notifier_max_retries: 0
+            notifier_topic: alarming
+          api:
+            user_alarm_quota: 10
+            project_alarm_quota: 10
+            alarm_max_actions: -1
+
 Development and testing
 =======================