mention the luks crypto at the end of the robot procedure

/cc @lavamind

howto/new-machine-hetzner-robot.md

@@ -93,6 +93,17 @@ with:
 
 ... and check the fingerprint against the email provided by Hetzner.
 
+Do a reboot before continuing with the install:
+
+    reboot
+
+You will need to enter the LUKS passphrase generated by the installer
+through SSH and the `dropbear-initramfs` setup. The LUKS password and
+the SSH keys should be available in the installer backlog. If that
+fails, then you can either try to recover from the out of band
+management (KVM, or serial if available), or scrutinize the logs for
+errors that could hint at a problem, and try a reinstall.
+
 See [howto/new-machine](howto/new-machine) for post-install configuration steps, then follow
 [howto/new-machine-mandos](howto/new-machine-mandos) for setting up the mandos client on this host.