docs(MIGRATION): add preset information for addon-backgrounds in 6.1
docs(MIGRATION): add preset information for addon-backgrounds in 6.1

storybooks/storybook,storybooks/storybook,storybooks/react-storybook,storybooks/storybook,storybooks/react-storybook,kadirahq/react-storybook,storybooks/storybook,storybooks/storybook,storybooks/storybook,storybooks/react-storybook,kadirahq/react-storybook,storybooks/storybook,storybooks/react-storybook