Add st2chatops documentation

Based on StackStorm/stackstorm-k8s#55

docs/source/install/k8s_ha.rst

@@ -351,6 +351,12 @@ Having ``1`` st2garbagecollector replica for K8s Deployment is enough, consideri
 By default this process does nothing and needs to be configured in st2.conf settings (via ``values.yaml``).
 Purging stale data can significantly improve cluster abilities to perform faster and so it's recommended to configure st2garbagecollector in production.
 
+`st2chatops <https://docs.stackstorm.com/chatops/index.html>`_
+______________________________________________________________
+StackStorm ChatOps service, based on hubot engine, custom stackstorm integration module and preinstalled list of chat adapters.
+Due to Hubot limitation, st2chatops doesn't provide mechanisms to guarantee high availability and so only single ``1`` node of st2chatops is deployed.
+This service is disabled by default. Please refer to Helm ``values.yaml`` about how to enable and configure st2chatops with ENV vars for your preferred chat service.
+
 `MongoDB HA ReplicaSet <https://github.com/helm/charts/tree/master/stable/mongodb-replicaset>`_
 ________________________________________________________________________________________________
 StackStorm works with MongoDB as a database engine. External Helm Chart is used to configure MongoDB HA `ReplicaSet <https://docs.mongodb.com/manual/tutorial/deploy-replica-set/>`_.