Added README.txt info about building from source
Added README.txt info about building from source

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