InstallTroubleshooting: correct table of contents Change-Id: I39a39a364dfc9a785eb3af758e4826b9495719f0 Reviewed-on: https://go-review.googlesource.com/c/wiki/+/623696 Commit-Queue: Ian Lance Taylor <iant@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Auto-Submit: Ian Lance Taylor <iant@golang.org>