content: add comment about << in range example

The 'Range Continued' code example uses a left shift operator.
Some people are unfamiliar with shift, and being puzzled about
what it means can distract from the point--which is range.

Per a suggestion from gri, this adds a small comment to show that
it's equivalent to 2**n.

Fixes golang/go#14241

Change-Id: If0bcfad85390db96f9f9c4295dc18f34410cb494
Reviewed-by: Robert Griesemer <>
1 file changed