Add description to Gold

BUG=skia:
R=hcm,jcgregorio
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2406753002
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=2406753002

Review-Url: https://codereview.chromium.org/2406753002
1 file changed