Add autoconf as required dependency for macOS

README.md

@@ -54,7 +54,7 @@ Please select your operating system:
 #### On macOS (homebrew)
 
 ``` sh
-brew install automake pkg-config python cmake yasm
+brew install automake autoconf@2.13 pkg-config python cmake yasm
 brew install gstreamer gst-plugins-base gst-plugins-good       gst-plugins-bad gst-plugins-ugly gst-libav gst-rtsp-server       --with-orc -with-libogg --with-opus --with-pango --with-theora       --with-libvorbis
 pip install virtualenv
 ```