crackfortran.py is not included in our doc build nor are the doctests run in CI. Trying the doctest locally passes, so putting this in.

Thanks @eric-wieser

Huh, I thought we found in one of @melissawm's PRs that refguide was still going through this file.

Currently it does not, at least not via python runtests.py --refguidecheck.

It will if we add f2py.crackfortran to refguidecheck here, but then we will have to fix the non-compliant module docstring and add >>> from numpy.f2py.crackfortran import getlincoef to the new doctest.

xref gh-15845 to replace refguidecheck with a better supported solution.