Update README.md add license button (brisbanesocialchess#354)

Author: jbampton

README.md

@@ -9,6 +9,7 @@ Welcome to the source code repository for the Brisbane Social Chess website.
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+[![GitHub License](https://img.shields.io/github/license/brisbanesocialchess/brisbanesocialchess.github.io)](LICENSE)
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