Add User Groups to README

Author: nikhita

README.md

@@ -15,7 +15,7 @@ For more specific topics, try a SIG.
 
 ## Governance
 
-Kubernetes has three types of groups that are officially supported:
+Kubernetes has the following types of groups that are officially supported:
 
 * **Committees** are named sets of people that are chartered to take on sensitive topics.
   This group is encouraged to be as open as possible while achieving its mission but, because of the nature of the topics discussed, private communications are allowed.
@@ -30,6 +30,9 @@ Kubernetes has three types of groups that are officially supported:
 * **Working Groups** are temporary groups that are formed to address issues that cross SIG boundaries.
   Working groups do not own any code or other long term artifacts.
   Working groups can report back and act through involved SIGs.
+* **User Groups** are groups for facilitating communication and discovery of information related to
+  topics that have long term relevance to large groups of Kubernetes users.
+  They do not have ownership of parts of the Kubernetes code base.
 
 See the [full governance doc](governance.md) for more details on these groups.