Add doc link to README.

README

@@ -13,6 +13,18 @@ will also support Hermite and nonconforming elements.
 
 For more information, visit http://www.fenicsproject.org
 
+
+Documentation
+=============
+
+The FIAT documentation can be viewed at
+http://fenics-fiat.readthedocs.org/.
+
+.. image:: https://readthedocs.org/projects/fenics-fiat/badge/?version=latest
+:target: http://fenics.readthedocs.io/projects/fiat/en/latest/?badge=latest
+:alt: Documentation Status
+
+
 License
 =======
 
@@ -29,9 +41,9 @@ License
   You should have received a copy of the GNU Lesser General Public License
   along with this program. If not, see <http://www.gnu.org/licenses/>.
 
+
 Dependencies
 ============
 
-#. Python, version 2.7 or later
-
-#. The Python modules NumPy and SymPy
+#. Python 2.7 or later
+#. The Python modules NumPy, SymPy and six