FAQ: update "shell vs. Python" section

[andychu]

Should you rewrite in Python?

http://www.oilshell.org/blog/2021/01/why-a-new-shell.html#shouldnt-scripts-over-100-lines-be-rewritten-in-python-or-ruby

Perhaps more convincing top level points

• tl;dr meme: Instead of writing 1200 lines of Python, it's better to write 300 lines of Python and 200 lines of shell.
• You are encouraged to use Python and Ruby when writing shell. Factoring into processes (written in different languages) is a Unix design skill.

[andychu]

some representative feedback: https://lobste.rs/s/p1hict/zxpy_tool_for_shell_scripting_python#c_0vsjuv