Clarify that published pack files are aarch64 (but 'work' on x86)

Clang binaries from the pack files will run on x86, with some performance penalty. Just wanted to note that.

README.md

@@ -27,6 +27,10 @@ bash ./link.sh --and-run clang --version
 ### x86-64
 Requirements: `elfshaker`, `wget`, `git`, `docker`
 
+Please note, that so far, moment packs are only published for aarch64 binaries.
+However, these binaries can run under qemu with some performance impact. For
+small code fragments, or some use cases, the impact may be tolerable.
+
 Replace `YYYYMM` below with the month and year for which you wish to fetch builds.
 ```bash
 mkdir -p manyclangs/elfshaker_data/packs manyclangs/bin