Fanoush: I've looked again at the README file and discovered the reason for my confusion regarding use of the word "either." You quote the sentence as:

"root device can be set either by linux flasher on PC over USB cable <step how to do it> or directly on device via cal-tool command <step how to do it>"

The fact that the <step how to do it> instructions occur on separate lines caused me to not read the ROOT DEVICE instruction as an intregal sentence. Sorry.

Also, presumably while you were sleeping last night (and I have to assume that you do sleep, though it's not always apparent from your prompt responses on the forum), I did try out your clarified instructions for copying the "bootmenu.conf.n770.example" file to "bootmenu.conf," which I then customized and reflashed, and the whole process worked fine on my 770. It was quite easy. Thanks again.