runtime: revise the document of Version() Fixes issue 7701. (again, differently)
runtime: revise the document of Version()
Fixes issue 7701. (again, differently)

LGTM=rsc
R=iant, rsc
CC=golang-codereviews
https://codereview.appspot.com/94560043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang