Say where the transparent pixel is from

go/favicon/favicon.go

	"github.com/golang/groupcache/lru"
)
// from https://commons.wikimedia.org/wiki/File:1x1.png
var transparentPixelPNG = []byte{
	0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d,
	0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,