message: Actually document salsa::requires
diff: @@ -46,6 +46,14 @@ mod query_group;
  ///
  /// Here is a list of legal `salsa::XXX` attributes:
  ///
  +/// - Query group attributes: apply to the trait itself
  +/// - `#[salsa::requires(OtherGroup)]` -- makes `OtherGroup` a
  +/// private dependency of the current group. That means that
  +/// functions that implement queries have `: OutherGropup` bound
  +/// on the database argument. This is similar to just making `OtherGroup`
  +/// a super trait, with a difference that users of the query group don't
  +/// get access to `OtherGroup` automatcally, which would be the case with
  +/// a super trait.
  /// - Storage attributes: control how the query data is stored and set. These
  /// are described in detail in the section below.
  /// - `#[salsa::input]`
  