Updating the docs to correct the signature of FFTW.
Updating the docs to correct the signature of FFTW.

jonathanessen/pyFFTW,jonathanessen/pyFFTW,drwells/pyFFTW,hgomersall/pyFFTW,jonathanessen/pyFFTW,drwells/pyFFTW,frederikhermans/pyfftw-arm,simudream/pyFFTW,hgomersall/pyFFTW,simudream/pyFFTW,hgomersall/pyFFTW,simudream/pyFFTW,frederikhermans/pyfftw-arm,drwells/pyFFTW,simudream/pyFFTW,drwells/pyFFTW