doc: add a remark on the new scoring method

doc/acceptance.md

@@ -13,6 +13,8 @@ The Acceptance process slightly differs whether you are a project's *developer*
 
 - The **Score** is computed by counting the current number of approvals from the project *developers*.
 
+Note: there is no real replacement for downvotes (:thumbsdown:) from the old method: this action is merged with the unresolved thread requirement.
+
 #### Old method
 
 - The **Score** is computed by comparing the number of :thumbsup: and :thumbsdown: given to the MergeRequest.