document master image creation

[Fathi Boudra]

http://lists.linaro.org/pipermail/linaro-dev/2011-December/009053.html

> > Is the official documentation to create a master image available on
> > https://wiki.linaro.org/Platform/Validation/Specs/MasterBootImage ?
> > If it's the case, we should convert it to a step by step how to and
> > link it to Validation knowledge base.
> >
> While that outlines what the end result should be, and details a few
> commands, it is by no means complete. I shall add the step by step
> instructions.

Some information are available on https://wiki.linaro.org/Platform/Validation/LAVA/Documentation#Creating_a_master_image
Maybe it's just a matter to check accuracy.

I'm in favor to split this section into a separate wiki page and include it into the above page.

[Spring Zhang (qzhang)]

I copied the wiki steps to http://lava-dispatcher.readthedocs.org/en/latest/installation.html#creating-a-sd-mmc-card-with-master-image, see if it needs a separate document

[Dave Pigott (dpigott)]

Added this page to rtfd: http://lava.readthedocs.org/en/latest/lava-image-creation.html