Match Windows 11 arm64 ISO names on arm64 hosts

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -24,8 +24,9 @@ Download or check selected targets:
 
 The Windows installation ISO is not downloaded because Microsoft's temporary
 download URLs expire. Place it manually in `install-iso/`; the script finds it
-automatically by matching `Win`, `11`, `x64` and `.iso` in that order
-(`*Win*11*x64*.iso`, case-insensitive). If several files match, the highest
+automatically by matching `Win`, `11`, the architecture (`x64`, or `arm64` on
+arm64 hosts) and `.iso` in that order (`*Win*11*x64*.iso` or
+`*Win*11*arm64*.iso`, case-insensitive). If several files match, the highest
 version-sorted name is used. Check which file was picked with
 `./download-images.sh --print-path windows11 --iso`.
 
@@ -47,7 +48,7 @@ The Windows target prints the QCOW2 path by default. Add `--iso` to print its
 manually supplied installation ISO path. The QCOW2 is named after the detected
 ISO (for example `Win11_25H2_English_x64_v2.iso` →
 `base-qcow2/Win11_25H2_English_x64_v2.qcow2`); if no ISO is present, an
-existing `*Win*11*x64*.qcow2` in `base-qcow2/` is used instead.
+existing `*Win*11*x64*.qcow2` (`*Win*11*arm64*.qcow2` on arm64) in `base-qcow2/` is used instead.
 
 Download URLs can be overridden with `DEBIAN_IMAGE_URL`, `ALMA_IMAGE_URL`,
 `FEDORA_IMAGE_URL`, `UBUNTU_IMAGE_URL`, and `VIRTIO_WIN_ISO_URL`. Each may