Add RNA name config to README.

README.md

@@ -65,6 +65,7 @@ Contains everything for the video demonstrations.
 * The RNA comes with SaltStack and SSH installed.
 * You can login using the `rna` user with the same password.
 * Upon first startup:
+  * Make sure that the hostname is updated (edit `/etc/hostname`) and the Salt `minion_id` is set appropriately (edit `/etc/salt/minion_id`).
   * Enter root mode with `sudo -i`
   * Run `salt-call test.ping` once.
   * Inside the RNA-Master, accept the key using `salt-key -L` and afterwards `salt-key -a` for the specific key.