doc: put a 'Last update on: timestamp' in footer

Change-Id: I8cf2e1dfe8836273991c278e2c7e68c7e7bad9fd
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/doc/conf.py b/doc/conf.py
index a309168..ecd8618 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -148,7 +148,7 @@
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-#html_last_updated_fmt = '%b %d, %Y'
+html_last_updated_fmt = '%b %d, %Y'
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.