-The new source format is [Sphinx](http://sphinx-doc.org), a documentation
-build tool written in [Python](http://python.org), which you will need to
-install if you want to build the document. You can find the complete
-installation instructions
-[here](http://www.sphinx-doc.org/en/stable/install.html).
+As well as these document sources, you will need:
+
+* Sphinx. You can find the complete installation instructions
+ [here](http://www.sphinx-doc.org/en/stable/install.html).
+
+* [Blockdiag](https://pypi.python.org/pypi/blockdiag) is used for some of
+ the diagrams.
+
+* To create the HTML version, you'll need a recent (>=0.7.8) version of the
+ [Alabaster](https://pypi.python.org/pypi/alabaster) theme.
+
+If you have `pip`, this command will be all you need:
+
+ pip install -U sphinx blockdiag alabaster