The phrase "couple X" is considered colloquial, so make that "a couple of X".
Also move the start of a sentence to a new line in a couple of places
for easier editing, in one place thereby removing two spaces after a period.

Change-Id: If5ef05eb496afc235f8f0134c4e7346375a65181
Reviewed-on: https://go-review.googlesource.com/112176Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>