Rename exercises dir

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

topics/containers/running_containers.md

@@ -0,0 +1,18 @@
+## Running Containers
+
+### Objective
+
+Learn how to run, stop and remove containers
+
+### Requirements
+
+Make sure Podman or Docker (or any other containers engine) is installed on your system
+
+### Instructions
+
+1. Run a container using the latest nginx image
+2. List the containers to make sure the container is running
+3. Run another container but this time use ubuntu latest and attach to the terminal of the container
+4. List again the containers. How many containers are running?
+5. Stop the containers
+6. Remove the containers