Enhance markdown in monailabel notebooks

[KumoLiu]

Description

Add notes in monailabel related notebooks to tell users terminate the kernel before closing the notebook to avoid port already used issue.

Checks

• [ ] Avoid including large-size files in the PR.
• [ ] Clean up long text outputs from code cells in the notebook.
• [ ] For security purposes, please check the contents and remove any sensitive info such as user names and private key.
• [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use relative paths for tutorial repo files (3) put figure and graphs in the ./figure folder
• [ ] Notebook runs automatically ./runner.sh -t <path to .ipynb file>

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[tangy5]

The notes and added statements look good. The monailabel notebooks can not be included in the notebook tests, before we listed them in the test file. Thanks for the PR.