Update README.md

Author: danielsmith-eu

README.md

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 # home-assistant-themeparks-integration
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+[![hacs_badge](https://img.shields.io/badge/HACS-Custom-41BDF5.svg?style=for-the-badge)](https://github.com/hacs/integration)
+
 A Home Assistant integration that shows Theme Park waiting times using the ThemeParks.wiki API
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+Add using HACS.