Add some docs about PIL / Pillow (ref #22).

docs/index.rst

@@ -60,9 +60,31 @@ Dependencies
 - Clint
 - Jinja2
 - Pilkit
-- Python Imaging Library (PIL / Pillow)
+- Python Imaging Library (PIL / Pillow, see below)
 - Python Markdown
 
+PIL or Pillow ?
+~~~~~~~~~~~~~~~
+
+PIL_ is almost dead, the last release was in 2009. If possible you should
+prefer to use Pillow_, a fork of PIL which is actively developped, with
+packaging improvements, Python 3 compatibility, etc.
+
+You can install Pillow with ``pip install Pillow``, preferably in a
+virtualenv_. To have JPG and PNG support, you must first install the
+developpement packages of libjpeg, freetype2 and zlib.
+
+- For Debian/Ubuntu, this is possible with::
+
+    apt-get build-dep python-dev python-imaging
+
+- For Archlinux, there is a package_ for sigal in the AUR which already uses
+  Pillow.
+
+.. _PIL: http://www.pythonware.com/products/pil/
+.. _Pillow: https://github.com/python-imaging/Pillow
+.. _package: https://aur.archlinux.org/packages/sigal/
+.. _virtualenv: http://www.virtualenv.org/
 
 How to Use
 ----------