time: add note about Parse()'s choice of default year
time: add note about Parse()'s choice of default year

R=rsc
CC=golang-dev
https://codereview.appspot.com/7101046

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