Add buymeacoffee

Finally, in need of some real coffee ;=))

Author: khoih-prog

README.md

@@ -5,6 +5,9 @@
 [![contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat)](#Contributing)
 [![GitHub issues](https://img.shields.io/github/issues/khoih-prog/Portenta_H7_AsyncWebServer.svg)](http://github.com/khoih-prog/Portenta_H7_AsyncWebServer/issues)
 
+<a href="https://www.buymeacoffee.com/khoihprog6" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/v2/default-yellow.png" alt="Buy Me A Coffee" style="height: 60px !important;width: 217px !important;" ></a>
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