Add the release notes for bitcoin-satellite v0.2.3

doc/release-notes/satellite/release-notes-0.2.3.md

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+Bitcoin Satellite 0.2.3 Release Notes
+====================
+
+Bitcoin Satellite version 0.2.3 is now available. This minor release includes
+improvements and bug fixes.
+
+Please report bugs using the issue tracker:
+
+  <https://github.com/Blockstream/bitcoinsatellite/issues>
+
+Alternatively, contact us at:
+
+  - <https://help.blockstream.com/>
+  - #blockstream-satellite IRC channel on freenode
+
+How to Upgrade
+==============
+
+The easiest way to upgrade is by using
+[`blocksat-cli`](https://blockstream.github.io/satellite/doc/quick-reference.html),
+the Blockstream Satellite command-line interface (CLI). Assuming you already
+have it installed, run:
+
+```
+blocksat-cli deps update --btc
+```
+
+Otherwise, you can [install the
+CLI](https://blockstream.github.io/satellite/doc/quick-reference.html#cli-installation-and-upgrade)
+and run the above command.
+
+Alternatively, you can upgrade Bitcoin Satellite manually by running the
+following commands:
+
+Ubuntu:
+```
+add-apt-repository ppa:blockstream/satellite
+apt-get update
+apt-get install --only-upgrade bitcoin-satellite
+```
+
+Debian:
+```
+add-apt-repository https://aptly.blockstream.com/satellite/debian/
+apt-key adv --keyserver keyserver.ubuntu.com \
+    --recv-keys 87D07253F69E4CD8629B0A21A94A007EC9D4458C
+apt-get update
+apt-get install --only-upgrade bitcoin-satellite
+```
+
+Raspbian:
+```
+add-apt-repository https://aptly.blockstream.com/satellite/raspbian/
+apt-key adv --keyserver keyserver.ubuntu.com \
+    --recv-keys 87D07253F69E4CD8629B0A21A94A007EC9D4458C
+apt-get update
+apt-get install --only-upgrade bitcoin-satellite
+```
+
+Fedora:
+```
+dnf copr enable blockstream/satellite
+dnf upgrade bitcoin-satellite
+```
+
+CentOS:
+```
+yum copr enable blockstream/satellite
+yum upgrade bitcoin-satellite
+```
+
+Compatibility
+==============
+
+Bitcoin Satellite 0.2.3 is supported and tested on the following Linux
+distributions:
+
+- Ubuntu LTS (18.04 and 20.04).
+- Fedora (33 and 34).
+- Debian (10 and 11).
+- Raspberry Pi OS (10 and 11).
+- CentOS 8.
+
+Bitcoin Core Version
+==============
+
+Bitcoin Satellite is a fork of Bitcoin Core. This specific release (version
+0.2.3) is based on Bitcoin Core 22.0.
+
+Notable changes
+===============
+
+SIMD Compatibility
+-----------------------------------
+
+Bitcoin Satellite uses a SIMD-accelerated GF(256) Galois Field implementation
+supporting the AVX2, SSSE3, and ARM Neon instruction sets. In runtime, the gf256
+module detects whether the running machine features any of the supported SIMD
+instruction sets and invokes the fastest available implementation. Nevertheless,
+in addition to the runtime detection, the build system must also be configured
+correctly. In particular, the build must restrict the usage of SIMD instructions
+to the functions called conditionally depending on the instruction set
+availability. Meanwhile, all other parts of the gf256 code (executed
+unconditionally) shall not contain machine-specific SIMD instructions.
+Otherwise, they can lead to illegal instruction errors when running on
+incompatible machines. This requirement was failing on the previous package
+version (Bitcoin Satellite v0.2.2). For example, the former package would crash
+on a host supporting SSSE3 but not AVX2.
+
+This release fixes SIMD incompatibilities on the gf256 implementation by
+separating it into multiple SIMD-specific sources: `gf256_avx2`, `gf256_ssse3`,
+and `gf256_neon`. In the new version, the build system enables AVX2 instructions
+only when compiling `gf256_avx2.cpp`. Likewise, it allows SSSE3 instructions
+only on `gf256_ssse3`, and so on. The program detects whether the
+AVX2/SSSE3/NEON sets are available in runtime and invokes the appropriate
+implementation. Meanwhile, the base `gf256` implementation (executed
+unconditionally) does not use any machine-specific SIMD instructions.
+
+0.2.3 Changelog
+=================
+
+### Bitcoind
+- Print the Bitcoin Satellite version on initialization and the version command.
+
+### FEC
+- Fix the compilation of SIMD-accelerated gf256 calculations.
+- Compile gf256 with SSSE3 and SSE2 instead of SSE3 when applicable.
+- Support gf256's Neon implementation on AArch32.
+
+### Transaction Compression
+- Fix compression ambiguity on TxOuts with code 24.
+- Support ending height on the `testcompression` RPC.
+
+### UDP Multicast Rx
+- Allow re-download of an out-of-order Rx block if not saved to the database.
+- Reload the disk-stored partial blocks on a background task.
+- Process disk-imported partial blocks immediately when fully decodable.
+- Process the block as a tip block if at least one message carries the tip flag.
+- Add removed state to partial blocks and prevent repeated processing attempts.
+- Do not exit if the receive buffer size configuration fails.
+
+### UDP Multicast Tx
+- Add option to specify the transaction compression scheme on RPC `txblock`.
+- Add option to save the UDP Multicast Tx window state using LevelDB.
+- Restore the Tx window state using parallel asynchronous workers.
+- Fix unnecessary polling for write space executed for empty Tx queues.