docs: adjust filenames to match the docs

docker-compose-db.yml

@@ -0,0 +1,16 @@
+version: '3'
+
+services:
+  postgres:
+    image: postgres:alpine
+    restart: unless-stopped
+    volumes:
+      - db-data:/var/lib/postgresql/data
+    ports:
+      - 5432:5432
+    environment:
+      - POSTGRES_DB=planka
+      - POSTGRES_HOST_AUTH_METHOD=trust
+
+volumes:
+  db-data: