Codex 用ファイル追加 (#346) (#347)

#346

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #347

docs/commands.md

@@ -0,0 +1,29 @@
+# Commands
+
+## Backend
+
+```sh
+cd backend
+bundle install
+bundle exec rails db:migrate
+bundle exec rspec
+bundle exec rails routes
+```
+
+## Frontend
+
+```sh
+cd frontend
+npm install
+npm run dev
+npm run build
+npm run lint
+npm test
+```
+
+### Full verification
+
+```sh
+cd backend && bundle exec rspec
+cd ../frontend && npm run build && npm run lint
+```