Documented required version of sphinx

DEPENDS.txt

@@ -56,3 +56,10 @@ Testing requirements
       A Python Unit Testing Framework
 * `Coverage.py <http://nedbatchelder.com/code/coverage/>`__
       A tool that generates a unit test code coverage report
+
+
+Documentation requirements
+--------------------------
+
+`sphinx >= 1.3 <http://sphinx-doc.org/>`_ is required to build the
+documentation.

doc/README.md

@@ -2,7 +2,7 @@
 To build docs, run `make` in this directory. `make help` lists all targets.
 
 ## Requirements ##
-Sphinx and Latex is needed to build doc.
+Sphinx (>= 1.3) and Latex is needed to build doc.
 
 **Sphinx:**
 ```sh