Warn if default numpy.int is 32 bit, or document it. #14029
Description
Related to #13961 (comment)
The doctests would fail if the default numpy.int is 32 bits long. We should either document this or have a step somewhere for pytest to warn, maybe something along the lines of:
if np.iinfo(np.int).dtype != np.int64:
warn(UserWarning, "Your default numpy int is a 32 bit one, it may be because you are "
"running a 32 bit Python (or more complicated if you're on Windows "
"or Mac. This causes some docstring tests to fail on your machine....")