message: Add note about branch releases
diff: seen when creating large Realm files on 32 bit OS.
  PR [#2795](https://github.com/realm/realm-core/pull/2795).
  +**Note: This is a hotfix release built on top of 2.9.1. The above fixes are not present in version 3.0.0.**
  +
  ----------------------------------------------
  # 2.9.1 Release notes
  .tar.gz files rather than .tar.xz files, with the exception of the aggregate
  realm-core-cocoa-VERSION.tar.xz archive, which remains as a .tar.xz file.
  +**Note: This is a hotfix release built on top of 2.9.0. The above fixes are not present in version 3.0.0.**
  +
  ----------------------------------------------
  # 2.9.0 Release notes
  