Enhanced readme

README.md

@@ -9,7 +9,10 @@ packaged on PyPi. You should clone the project to your local machine and
 do an [editable install](https://pip.pypa.io/en/stable/topics/local-project-installs/#editable-installs) 
 in a [virtual environment](https://docs.python.org/3/library/venv.html).
 
+Note: You will also need ffmpeg.
+
 ```sh
+$ brew install ffmpeg
 $ git clone https://git.squad51.us/jamie/ucsinfer.git
 $ git submodule sync
 $ python -m venv .venv