suggest: update webpage re Python

[nbehrnd]

The webpage https://babluboy.github.io/bookworm/#install explicitly describes Python2 as dependency (first bullet list, and the command for the CLI to let apt resolve all dependencies in one run).

There is no obvious file I associate with the content of the source code; for this, my criterion with searchmonkey was to find any file (no constraint regarding the file extension) with one or more occurrences of Then execute the following commands. On the other hand, Python2 no longer is in active development, and https://github.com/babluboy/bookworm/tree/master/data/scripts/mobi_lib lists many scripts with the commit message of Update mobi lib for Python 3 by [2020-04-12 Sun].

If building the executable only with the libraries branch of Python3 works, I suggest that the web page is going to be updated accordingly, to equally reflect this very transition.