Added note in docs that this is the dev branch.

docs/menu.rst

@@ -3,7 +3,11 @@
     1) `Overview`_
     2) `Concepts`_
     3) `API reference`_
-    
+
+Note: This is the documentation for the *dynamic_alloc_dev* development branch. See here for the 
+documentation for the latest stable version:
+http://koti.kapsi.fi/~jpa/nanopb/docs/index.html
+
 .. _`Overview`: index.html
 .. _`Concepts`: concepts.html
 .. _`API reference`: reference.html