Rename exercises dir

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

topics/devops/containerize_app.md

@@ -0,0 +1,14 @@
+## Containerize an Application
+
+1. Clone an open source project you would like to containerize. A couple of suggestions:
+
+```
+https://github.com/bregman-arie/node-hello-world
+https://github.com/bregman-arie/flask-hello-world
+```
+2. Write a Dockerfile you'll use for building an image of the application (you can use any base image you would like)
+3. Build an image using the Dockerfile you've just wrote
+4. Verify the image exists
+5. [Optional] Push the image you've just built to a registry
+6. Run the application
+7. Verify the app is running