Rename exercises dir

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

topics/kubernetes/pods_01.md

@@ -0,0 +1,11 @@
+## Pods 01
+
+#### Objective
+
+Learn how to create pods
+
+#### Instructions
+
+1. Choose a container image (e.g. redis, nginx, mongo, etc.)
+2. Create a pod (in the default namespace) using the image you chose
+3. Verify the pod is running