update release notes

Author: akrzemi1

doc/92_relnotes.qbk

@@ -37,7 +37,7 @@
   * Construct `o = u`, where `o` is of type `optional<T>` and `u` is of type `U` convertible to `T`,
     does not create a temporary `T`.
 
-* In the said implementation, added a conversion from `optional<T>&` to `optional<T&>`.
+* In the said implementation, added a conversion from `optional<T>&` to `optional<T&>`. This addresses [@https://github.com/boostorg/optional/issues/142 issue #142].
 
 * `none_t` is now `std::equality_comparable`, which means that `none_t` and `optional<T>`
   model concept `std::equality_comparable_with` (for `std::equality_comparable` `T`s),