update readme to better document imagemagick

README.rst

@@ -75,6 +75,16 @@ For advanced image processing, you will need one or several of the following pac
 - `Scikit Image`_ may be needed for some advanced image manipulation.
 - `OpenCV 2.4.6`_ or a more recent version (one that provides the package ``cv2``) may be needed for some advanced image manipulation.
 
+Once you have installed it, ImageMagick will be automatically detected by MoviePy, (except for windows users and Ubuntu 16.04LTS users).
+
+For Windows users, before installing MoviePy by hand, go into the ``moviepy/config_defaults.py`` file and provide the path to the ImageMagick binary called `convert`. It should look like this ::
+    
+    IMAGEMAGICK_BINARY = "C:\\Program Files\\ImageMagick_VERSION\\convert.exe"
+
+For Ubuntu 16.04LTS users, after installing MoviePy on the terminal, IMAGEMAGICK will not be detected by moviepy. This bug can be fixed. Modify the file in this directory: /etc/ImageMagick-6/policy.xml, comment out the statement <!-- <policy domain="path" rights="none" pattern="@*" /> -->.
+
+PyGame_ is needed for video and sound previews (useless if you intend to work with MoviePy on a server but really essential for advanced video editing *by hand*).
+
 For instance, using the method ``clip.resize`` requires that at least one of Scipy, PIL, Pillow or OpenCV is installed.