Some fixes and added debug information to documentation

README.md

@@ -83,6 +83,22 @@ If this command fails, configure the remote account's `sudoers` entry for the
 necessary `zfs` commands with `NOPASSWD` before running the migration. Do not
 put a password in the script or on its command line.
 
+Use the exact same account, hostname, key, and port in the script as in this
+successful test. For example, if `admin@new-server` succeeds, run:
+
+```bash
+bash zfs-move-over-ssh.sh \
+  -i ~/.ssh/zfs-migration \
+  tank \
+  admin@new-server \
+  backup/tank
+```
+
+Do not substitute `root@new-server` for `admin@new-server` unless a separate
+non-interactive key test succeeds for `root`. SSH keys and `sudo` permissions
+are configured per remote user, so a key that works for `admin` may be denied
+for `root`.
+
 `REMOTE_HOST` must be a complete hostname or address, such as
 `root@192.0.2.10` or `admin@new-server`. `root@` is invalid because it has no
 host after the `@`.