message: Doc: update ACK description in CONTRIBUTING.md
  as per and
diff: @@ -239,7 +239,10 @@ consensus to merge a pull request (remember that discussions may have been
  spread out over GitHub, mailing list and IRC discussions). The following
  language is used within pull-request comments:
  - - ACK means "I have tested the code and I agree it should be merged";
  + - (t)ACK means "I have tested the code and I agree it should be merged", involving
  + change-specific manual testing in addition to running the unit and functional
  + tests, and in case it is not obvious how the manual testing was done, it should
  + be described;
  - NACK means "I disagree this should be merged", and must be accompanied by
  sound technical justification (or in certain cases of copyright/patent/licensing
  issues, legal justification). NACKs without accompanying reasoning may be
  