Add titles in the untitled notebooks

[patel-zeel]

What is the issue?

• The website page for this repo is generated with quarto.
• Quarto renders notebooks nicely in HTML format e.g. Active Learning.
• Quarto needs to assign a title to each notebook to show it in the index. It does that in mainly two ways: i) Check for # Title in the first cell of the notebook; ii) Check for metadata, similar to https://github.com/nipunbatra/pml-teaching/blob/83edc6e340a66e51f89737687bf18d58e990fb91/notebooks/biased-mle-normal.ipynb#L7-L13
• A few notebooks do not have metadata or # titles and thus their names are not visible in the index.

What needs to be done?

• Check the index and identify the notebooks with missing titles.
• Add a meaningful # title to each such notebook.