python manual: Fix 'fftw*' output references in example

doc/languages-frameworks/python.md

···
   # Tests cannot import pyfftw. pyfftw works fine though.
   doCheck = false;
 
-  LDFLAGS="-L${pkgs.fftw}/lib -L${pkgs.fftwFloat}/lib -L${pkgs.fftwLongDouble}/lib"
-  CFLAGS="-I${pkgs.fftw}/include -I${pkgs.fftwFloat}/include -I${pkgs.fftwLongDouble}/include"
+  LDFLAGS="-L${pkgs.fftw.dev}/lib -L${pkgs.fftwFloat.out}/lib -L${pkgs.fftwLongDouble.out}/lib"
+  CFLAGS="-I${pkgs.fftw.dev}/include -I${pkgs.fftwFloat.dev}/include -I${pkgs.fftwLongDouble.dev}/include"
   '';
 
   meta = {