[llvm] [AArch64][Docs] Add release note for execute-only support on AArch64 (PR #134799)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Is there a description somewhere of why you're implementing this?  Last time we looked at this, we concluded it wasn't really useful.  See https://reviews.llvm.org/D48791 .

https://github.com/llvm/llvm-project/pull/134799