added platform specific notes to readme

README.md

@@ -1,2 +1,22 @@
 # eegsynth-matlab
 Converting real-time EEG into sounds and music
+
+## Platform specific notes for Mac OS X
+Compilation of the mex files requires that portmidi is present. This can be downloaded
+from http://portmedia.sourceforge.net/portmidi. Compilation of portmidi requires cmake.
+It is also possible to install a compiled version of portmidi using MacPorts ("sudo port
+install portmidi").
+
+Furthermore, for compilation you probably need to update the library path settings in
+compile\_midi.m
+
+## Platform specific notes for Microsoft Windows
+Precompiled mex file are provided, these are linked to a static version of portmidi.  To
+use these mex files in MATLAB, you might have to install the Microsoft Visual C++ 2010
+Redistributable Package, which is available from [1]. This package contains some
+additional system libraries that are used by MSVC 2010.
+
+[1] https://www.microsoft.com/en-us/download/details.aspx?id=5555
+
+## Platform specific notes for Linux
+Compilation on Linux requires the ALSA libraries to be installed.