fix(env): add postgres docker aliases

.env.example

@@ -19,6 +19,12 @@ DB_PASSWORD=change-me
 DB_HOST=db
 DB_PORT=5432
 
+# Required by the official PostgreSQL Docker image on first initialization.
+# Keep these in sync with DB_NAME, DB_USER, and DB_PASSWORD.
+POSTGRES_DB=cs_association
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=change-me
+
 # Redis / Celery
 REDIS_PASSWORD=change-me
 REDIS_URL=redis://:change-me@redis:6379/0