rebaseline_server: add download link for SKP diff patchfile

BUG=skia:1918
NOTREECHECKS=true
NOTRY=true
R=stephana@google.com
TBR=stephana
(SkipBuildbotRuns)

Author: epoger@google.com

Review URL: https://codereview.chromium.org/489183002
2 files changed