Update README.rst

Fix broken link

README.rst

@@ -9,7 +9,7 @@ https://www.unix-ag.uni-kl.de/~bloch/acng
 .. note::
 
     See the full `Salt Formulas installation and usage instructions
-    <http://docs.saltstack.com/topics/conventions/formulas.html>`_.
+    <http://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html>`_.
     
 
 Requirements