message: Add notes to the changelog
diff: ### Enhancements
  -* Lorem ipsum.
  +* Add support for `SharedGroup::try_begin_write()` and corresponding `try_lock()`
  + functionality in low level Mutex classes.
  + PR [#2547](https://github.com/realm/realm-core/pull/2547/files)
  + Fixes issue [#2538](https://github.com/realm/realm-core/issues/2538)
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