Mr. Chromebox is a developer who is saving us all a lot of time typing in commands with an all-in-one script. Go to the page for his Chrome OS firmware script and type out the command on that page (starting with cd; curl ...

You should see prompt similar to the one at left (but maybe not exactly; this is from a different device and time). You're going to choose "Install/Update Full ROM Firmware," which is usually the third option, by typing in "3" and hitting Enter.

When asked if you want to back up your firmware by the script, you should say (Y)es! Plug in a second USB drive (different than the one you're using for the CloudReady installer), select it when prompted, and continue along. Back up the firmware file to Drive or another safe location, as well.

Once the script is done installing the new firmware, enter "P" to power off.