print Notes heading only if there are any

bin/ansible-doc

@@ -83,7 +83,7 @@ def print_man(doc):
         print "%s\n" % textwrap.fill(tty_ify(desc), initial_indent=opt_indent,
                             subsequent_indent=opt_indent)
 
-    if 'notes' in doc:
+    if 'notes' in doc and len(doc['notes']) > 0:
         notes = "".join(doc['notes'])
         print "Notes:%s\n" % textwrap.fill(tty_ify(notes), initial_indent="  ",
                             subsequent_indent=opt_indent)