add release notes

.release-notes/4567.md

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+## Deterministic cerealisation for cross binary communication
+
+Pony built-in serialisation can now be used between binaries compiled with the same version of the pony compiler (this would likely result in segfaults previously). Cross binary serialisation will only work for binaries of the same bit width (32 bit vs 64 bit), data model (ilp32, lp64, or llp64), and endianness (big endian or little endian) but is not limited to a single platform (for example: one can mix and match x86_64 linux and aarch64 linux because they have the same bitwidth, data model, and endianness).