content/2012: prevent present from misinterpreting comment as title

Fixes golang/go#43455

Change-Id: I889038efc166b1fb404764f82726c36a1a69ae0d
Reviewed-on: https://go-review.googlesource.com/c/talks/+/284392
Reviewed-by: Rob Pike <r@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>