Inject the SSH public key into the Fedora and AlmaLinux seed ISOs

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

seediso/almalinux10/README.md

@@ -3,6 +3,10 @@
 This directory contains the cloud-init NoCloud configuration used by
 `run-almalinux10.py`.
 
+`build-seed.sh` injects your SSH public key into `user-data` (the `@SSH_PUBKEY@`
+placeholder): `$SSH_PUBKEY_FILE`, else the first `~/.ssh/id_*.pub`, else the first
+key offered by `ssh-agent`.
+
 After changing `user-data`, `meta-data`, or `network-config`, remove the old
 `seed.iso` and rebuild it: