Add a command line tool for people to perform subset selection with one line of bash code

[FanwangM]

This is good to have, but let's leave it to the last stage. An example can be found at https://github.com/theochem/B3clf.

[FanwangM]

This is too much work and does not help the audience. But we can do it in the future.

[PaulWAyers]

To the extent we decide to do this, we should use https://github.com/tiangolo/typer which makes it easy(ish). The "big brother" of this is fastapi which would build the webserver @FanwangM has talked about.