Update README.md

Author: TeaDrinkingProgrammer

README.md

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 # TeaDrinkingProgrammer-site
 This is the Github repo for my personal website: [TeaDrinkingProgrammer.github.io](https://TeaDrinkingProgrammer.github.io)
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+# Theme
+This website uses my [Tranquil theme](https://github.com/TeaDrinkingProgrammer/tranquil). If you want to use the theme, please refer to that repo.