sandbox/iirdes_test: improving help file
sandbox/iirdes_test: improving help file

jgaeddert/liquid-dsp,JayKickliter/liquid-dsp,JayKickliter/liquid-dsp,wangning223/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,JayKickliter/liquid-dsp,JayKickliter/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,JayKickliter/liquid-dsp