add brief readme for macos

Author: catfact

readme-macos.md

@@ -0,0 +1,15 @@
+to build and use `softcut_jack_osc` on macOS, JACK must be installed and running. also some packages dependencies need to be installed via macports or homebrew:
+
+```
+sudo port install jack
+sudo port install libsndfile1-dev
+sudo port install liblo
+```
+
+to use the software, `jackd` must be running:
+
+```
+jackd -d coreaudio 
+```
+
+and the selected audio device must have at least 2 channels of I/O. (i find it easiest to use an aggregate device on mac laptops.)