Add a link to the dylan domain docs

Add a link to the dylan domain docs

README.rst

@@ -1,6 +1,7 @@
 These are extensions for `Sphinx <http://sphinx.pocoo.org/>`_ that we use
 in the construction of our website and documentation.
 
-This repository is automatically pulled into the appropriate places as
+This repository is usually pulled into the appropriate places as
 a git submodule.
 
+See https://github.com/dylan-lang/sphinx-extensions/blob/master/sphinxcontrib/dylan/domain/reference.rst for documentation on the "dylan" Sphinx domain.