design/24543: general preemption discussion
design/24543: general preemption discussion

This expands the background of this design document to discuss
non-cooperative preemption in general. In particular, it relates it to
how desktop and server operating systems implement threads.

Updates golang/go#24543.

Change-Id: Ibcd1cff3f00ec9e153122d5eb21a9a1699630e34
Reviewed-on: https://go-review.googlesource.com/c/158860
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

golang/proposal,golang/proposal