doc: new document about compatibility of releases The doc is not linked anywhere yet; that will come later.
doc: new document about compatibility of releases
The doc is not linked anywhere yet; that will come later.

R=golang-dev, adg, gri, rsc, edsrzf
CC=golang-dev
http://codereview.appspot.com/5647050

gnanderson/go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,dsriram/golang,tv42/old-go,tv42/old-go,apparentlymart/golang,tv42/old-go,dsriram/golang,gnanderson/go,gnanderson/go,dsriram/golang,tv42/old-go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,tv42/old-go,gnanderson/go,gnanderson/go,dsriram/golang,gnanderson/go