Link to touchtests install docs in presubmit

This makes the failure message if you haven't set up the touchtests in
your chroot much more helpful.

BUG=b:160011461
TEST=`sudo mv /usr/bin/touchtests{,-foo}; ./tools/regression_test.sh`
    (in chroot)

Change-Id: Iac7abbd27cc8dee0f9ec8c43de15ff7210d7114f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/2762423
Tested-by: Harry Cutts <hcutts@chromium.org>
Auto-Submit: Harry Cutts <hcutts@chromium.org>
Commit-Queue: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
1 file changed