add postgresql docker service

Author: myty

.dockerignore

@@ -0,0 +1 @@
+.git

database.env

@@ -0,0 +1,3 @@
+POSTGRES_USER=unicorn_user
+POSTGRES_PASSWORD=magical_password
+POSTGRES_DB=rainbow_database

docker-compose.yml

@@ -6,3 +6,11 @@ services:
             dockerfile: Dockerfile
         ports:
             - "1993:1993"
+    database:
+        image: "postgres" # use latest official postgres version
+        env_file:
+            - database.env # configure postgres
+        volumes:
+            - database-data:/var/lib/postgresql/data/ # persist data even if container shuts down
+volumes:
+    database-data: # named volumes can be managed easier using docker-compose