[x/tour] content: clarify semantics of range clause
[x/tour] content: clarify semantics of range clause

Fixes golang/tour#560

Change-Id: I91255fe7ddb6df16268d6adc6afa2a502f1265f0
Reviewed-on: https://go-review.googlesource.com/c/125055
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
X-Tour-Commit: 0b2cf7c0845f35c40cf2d699f801671149e9e2cb

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website