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Update README.md
Merge pull request #8774 from Denisov21/patch-16

Update README.md
Merge pull request #8772 from adobe/larz/issue-8771

Transparent checkerboard for ImageViewer is now dark.
Merge branch 'master' into jeff/splitview-1x2
Merge branch 'jeff/splitview-1x2' into jeff/splitview-factory