Update README.md

Kubernetes/concepts/README.md

@@ -7,4 +7,9 @@
 2. Controller - manager
   - Node Controller
   - Replication controller
-  - 
+- continuously watches the status of the nodes
+- takes actions to remediate situation
+- A controller is a process that continuously monitors the state of different components and works towards bringing the whole system to the desired working state.
+- Node contoller monitors the node through kube-apisever.
+
+3.