README: add information how to use randseeds

Add some information as to how to use these seeds..

Reported-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Merge branch 'README-update' of https://github.com/nmenon/omap-seeds

* 'README-update' of https://github.com/nmenon/omap-seeds:
  README: add information how to use randseeds

Signed-of-by: Felipe Balbi <balbi@ti.com>