Change sprinkles readme so example works together

[samrobbins85]

The readme for sprinkles uses blue50, whereas the declaration uses blue-50 and the gray declaration doesn't exist. While this is just an example so not too important, it helps with initial setup that you can copy the code provided and everything will work.

[changeset-bot]

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Latest commit: 5c3e084

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[markdalgleish]

Thank you!