message: Add comments to port name suffix rule checker
  As requested in
diff: @@ -94,6 +94,9 @@ bool PortNameSuffixRule::IsSuffixCorrect(const absl::string_view suffix,
  {"output", {"o", "no", "po"}},
  {"inout", {"io", "nio", "pio"}}};
  + // At this point it is guaranteed that the direction will be set to
  + // one of the expected values (used as keys in the map above).
  + // Therefore checking the suffix like this is safe
  return suffixes.at(direction).count(suffix) == 1;
  }
  