build: trivial license clarification in main README
build: trivial license clarification in main README

manuts/liquid-dsp,wangning223/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,cjcliffe/liquid-dsp,manuts/liquid-dsp,wangning223/liquid-dsp,wangning223/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,jgaeddert/liquid-dsp,andrepuschmann/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,jgaeddert/liquid-dsp,biotrump/liquid-dsp,jgaeddert/liquid-dsp,jgaeddert/liquid-dsp,manuts/liquid-dsp,biotrump/liquid-dsp,manuts/liquid-dsp,cjcliffe/liquid-dsp,manuts/liquid-dsp,biotrump/liquid-dsp,biotrump/liquid-dsp,JayKickliter/liquid-dsp,cjcliffe/liquid-dsp,JayKickliter/liquid-dsp,JayKickliter/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,JayKickliter/liquid-dsp,JayKickliter/liquid-dsp,biotrump/liquid-dsp,jgaeddert/liquid-dsp