misc/nacl: add debugging instructions
misc/nacl: add debugging instructions

LGTM=dave, minux
R=golang-codereviews, dave, minux
CC=golang-codereviews, rsc
https://codereview.appspot.com/122570043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go