Merge bitcoin/bitcoin#24597: doc, guix: Include `arm64-apple-darwin` into codesigned archs

1f4801b6b1 doc, guix: Include arm64-apple-darwin into codesigned archs (Hennadii Stepanov)

Pull request description:

ACKs for top commit:
  fanquake:
    ACK 1f4801b6b1

Tree-SHA512: 6e0d5f463a97d3a87ce2c503a97762bd756ae44e1b8d343477de68fa4188f9be44752484a60ee08db389567ca456efb7789635ab921197b33eed974d0cee2f0b

contrib/guix/README.md

@@ -75,7 +75,7 @@ crucial differences:
 
 1. Since only Windows and macOS build outputs require codesigning, the `HOSTS`
    environment variable will have a sane default value of `x86_64-w64-mingw32
-   x86_64-apple-darwin` instead of all the platforms.
+   x86_64-apple-darwin arm64-apple-darwin` instead of all the platforms.
 2. The `guix-codesign` command ***requires*** a `DETACHED_SIGS_REPO` flag.
     * _**DETACHED_SIGS_REPO**_