docs: mention building for some HOSTs only in release-process.md

Author: UdjinM6

doc/release-process.md

@@ -97,6 +97,8 @@ Follow the relevant Guix README.md sections:
 - [Building](/contrib/guix/README.md#building)
 - [Attesting to build outputs](/contrib/guix/README.md#attesting-to-build-outputs)
 
+_Note: we build releases for some supported HOSTs only so either provide correct `HOSTS` variable or run `./contrib/containers/guix/scripts/guix-start` instead of `./contrib/guix/guix-build` when building binaries_
+
 ### Verify other builders' signatures to your own. (Optional)
 
 Add other builders keys to your gpg keyring, and/or refresh keys: See `../dash/contrib/builder-keys/README.md`.