Add the assignment to use Docker configs

[refs #2fed0ac6a5b6]

Author: jfahrer

swarm/assignment4.md

@@ -0,0 +1,9 @@
+## Make use of configurations
+* Replace the image for the db service
+  * Use `postgres:9.6-alpine`
+  * Keep the environment variables
+  * Mount the attached SQL file to `/docker-entrypoint-initdb.d/create_table.sql`
+* Make sure that no other service publishes port 80
+* Deploy the stack
+  * Use a new stack name if you previously deployed it
+  * Or delete the volumes from the node