Python vs IPython: recommend %cd, %env over !cd, !export...
Python vs IPython: recommend %cd, %env over !cd, !export
The quick overview mentioned `!cd DIR` among examples of shell
commands one might use —but that doesn't work as user would hope
(can only affect commands in same ! e.g. `!cd /; pwd`).
That's not as bad now that `!cd` prints a warning,
but IMHO better to provide the right mental model up front.
=> Replaced that with minimal motivation why `!cd` and `!export` can't work,
recommending some %magic alternatives;
moved it out of examples to not distract, and right before Magics section.
