Add the 2nd assignment

[refs #822c1b2c51b6]

Author: jfahrer

compose_example/assignment2.md

@@ -0,0 +1,15 @@
+## Integrate the load balancer
+* Add the required environment variable to the .env file
+  * Set PROXY_UPSTREAM to `webapp:9292`
+* Remove the `web` service definition
+* Add a new service definition
+  * Call it `lb`
+  * Use your load balancer image
+    * Or use jfahrer/lb:v2
+  * Depend on the service `webapp`
+  * Make sure to assign the PROXY_UPSTREAM environment variable
+  * Publish port 80
+* Stop publishing the `webapp` service
+* Start the services using docker-compose
+* Use your browser to verify it works
+  * http://localhost