Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/kubernetes/services_01.md

@@ -0,0 +1,11 @@
+## Services 01
+
+#### Objective
+
+Learn how to create services
+
+#### Instructions
+
+1. Create a pod running ngnix
+2. Create a service for the pod you've just created
+3. Verify the app is reachable