Document a bit more verbosely the purpose of generatePassword method.

Especially, explain what is meant by "last call".

slapos/recipe/librecipe/generic.py

@@ -125,6 +125,15 @@ class GenericBaseRecipe(object):
         'template/%s' % template_name)
 
   def generatePassword(self, len_=32):
+    """
+    The purpose of this method is to generate a password which doesn't change
+    from one execution to the next, so the generated password doesn't change
+    on each slapgrid-sr execution.
+
+    Currently, it returns a hardcoded password because no decision has been
+    taken on where a generated password should be kept (so it is generated
+    once only).
+    """
     # TODO: implement a real password generator which remember the last
     # call.
     return "insecure"