message: fix syntax notation
diff: @@ -97,7 +97,7 @@ macro_rules! params_internal {
  /// parameters of the query with a HashMap/similar. Their items follow the
  /// syntax:
  ///
  -/// [required|optional] key [=> value]
  +/// (required|optional) key [=> value]
  ///
  /// The first keyword is just to distinguish between a direct insert into the
  /// hashmap (required parameter), and an insert only if the value is `Some(...)`
  