docs: fix markdown format and add todo comment

Author: Henry Lee

docs/CONTRIBUTING.md

@@ -48,20 +48,30 @@ If additional steps are required after merging and deploying (e.g., add new conn
 
 ### 7. Wait for the review and merge.
 
+## Login to Airflow Web UI
+
+Ask maintainers for your Airflow account and credentials.
+
+<!--TODO: GitHub or Google OAuth login maybe a good way to reduce maintenance overhead, but it requires more setup. -->
+
 ## Convention
 
 ### Airflow Dags
+
 - Please refer to [「大數據之路：阿里巴巴大數據實戰」 讀書心得](https://medium.com/@davidtnfsh/%E5%A4%A7%E6%95%B0%E6%8D%AE%E4%B9%8B%E8%B7%AF-%E9%98%BF%E9%87%8C%E5%B7%B4%E5%B7%B4%E5%A4%A7%E6%95%B0%E6%8D%AE%E5%AE%9E%E8%B7%B5-%E8%AE%80%E6%9B%B8%E5%BF%83%E5%BE%97-54e795c2b8c) for naming guidelines.
 - Table name convention:
   ![img](https://miro.medium.com/max/1400/1*bppuEKMnL9gFnvoRHUO8CQ.png)
 
 ### Code Formatting
+
 Please run `make format` to ensure your code is properly formatted before committing; otherwise, the CI will fail.
 
 ### Commit Message
+
 It is recommended to use [Commitizen](https://commitizen-tools.github.io/commitizen/).
 
 ## Release Management (CI/CD)
+
 We use [Python CI] and [Docker Image CI] to ensure our code quality meets specific standards and that Docker images can be published automatically.
 
 When a pull request is created, [Python CI] checks whether the code quality is satisfactory. At the same time, we build a `cache` image using `Dockerfile` and a `test` image with `Dockerfile.test`, which are then pushed to the [GCP Artifact Registry].
@@ -106,4 +116,4 @@ config:
 [uv]: https://docs.astral.sh/uv/
 [Python CI]: https://github.com/pycontw/pycon-etl/actions/workflows/python.yml
 [Docker Image CI]: https://github.com/pycontw/pycon-etl/actions/workflows/dockerimage.yml
-[GCP Artifact Registry]: https://cloud.google.com/artifact-registry/
+[GCP Artifact Registry]: https://cloud.google.com/artifact-registry/

docs/DEPLOYMENT.md

@@ -36,7 +36,7 @@ docker-compose -f ./docker-compose.yml up
 ### 5. Check whether the services are up
 
 ```bash
-# For Airflow, the following services should be included: 
+# For Airflow, the following services should be included:
 # * airflow-api-server
 # * airflow-dag-processor
 # * airflow-scheduler
@@ -48,4 +48,5 @@ docker stats
 ```
 
 ### 6. Login to the service
-For security reasons, our Airflow instance is not publicly accessible. You will need an authorized GCP account to perform port forwarding for the webserver and an authorized Airflow account to access it.
+
+For security reasons, our Airflow instance is not publicly accessible. You will need an authorized GCP account to perform port forwarding for the webserver and an authorized Airflow account to access it.

docs/MAINTENANCE.md

@@ -17,10 +17,11 @@ du -a /var/lib/docker/overlay2 | sort -n -r | head -n 20
 ### 2. Show the folder size:
 
 ```bash
-du -hs 
+du -hs
 ```
 
 ### 3. Delete the large folders identified.
+
 ### 4. Check disk space:
 
 ```bash