add alembic and readme

docker-compose.yml

@@ -12,10 +12,12 @@ services:
 
   api:
     build: .
-    ports:
-      - "8000:8000"
     environment:
       DATABASE_URL: postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
+    ports:
+      - "8000:8000"
+    volumes:
+      - ./app/migrations/versions:/code/app/migrations/versions
     depends_on:
       - db