hterm: Add the final step to doc/embed.md

Change-Id: Ib9ed4ad5f088d18931f2c67fa15a7165178d285a
Reviewed-on: https://chromium-review.googlesource.com/209401
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>