Update 1.91.0 release notes for Boost.MSM (#618)

Author: chandryan

release-notes/boost_1_91_0.adoc

@@ -101,6 +101,8 @@ a `boost::tuple` (and similarly for the rest of affected class templates).
 ** Bug fixes (`backmp11`):
 *** Incorrect `FSM` type in calls to `on_entry(...)` and `on_exit(...)` (https://github.com/boostorg/msm/issues/167[#167])
 *** Completion events fire too often (https://github.com/boostorg/msm/issues/166[#166])
+*** Transitions in hierarchical state machines are not selected correctly (favor_compile_time) (https://github.com/boostorg/msm/issues/200[#200])
+*** `state_machine` cannot be moved (https://github.com/boostorg/msm/issues/205[#205])
 ** **Breaking change (`backmp11`)**: Direct access to the event pool is changed from `public` to `protected`,
 because manipulating it outside of the library code can lead to undefined behavior.