git: openjdk/shenandoah-visualizer: master: Move the screenshot to images

[duke]

Changeset: fed9b79f
Author:    Aleksey Shipilev <shade at redhat.com>
Date:      2020-11-16 20:19:16 +0000
URL:       https://github.com/openjdk/shenandoah-visualizer/commit/fed9b79f

Move the screenshot to images

= images/sample-screenshot.png