[oe] how to create a new layer

[Richard Cagley]

> One other thing to note - if there are overrides for the previous machine
> (e.g. in bbappends you may see _zedboard-zynq7) you should change
> these to _me so that they still apply.
>

What is the threshold for making a new machine? That is, if I just
have a .bbappend file I want, that should just involve creating a new
layer and putting the bbappend file in the correct location. I
shouldn't have to change anything else correct?

For instance, if I just want to change the kernel configuration with a
frag file I can put linux-xlnx_3.8.bbappedn in
meta-me/recipes-kernel/linux and that's all I need?

I guess I'm just confused at what point I actually need a new machine.