[docs] [issue38623] Python documentation should mention how to find site-packages

Inada Naoki <songofacandy@gmail.com> added the comment:

There is a specific question this change attempts to answer: "Where is the module I imported located in the file system?"

So `print(the_module.__file__)` is better answer. (or `pip list -v` if the module is third party package installed via pip). `python -m site` doesn't tell you where the imported module came from.

[3] https://docs.python.org/3/library/site.html#site.getusersitepackages

After merging PR 17858, you can use :ref:`site-commandline` for cross reference. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue38623> _______________________________________