README: update layer dependencies list
README: update layer dependencies list

* meta-initramfs is now required
* meta-oe is currently required but we should be able to remove this
  dependency fairly soon.

Signed-off-by: Paul Eggleton <737d4dae46a541673d7bf4e0d5b32714b16528d8@linux.intel.com>

bluelightning/meta-handheld,bluelightning/meta-handheld