doc: add Buy me a coffee button to readme

README.md

@@ -13,4 +13,6 @@ if you see it anywhere else, it's a scam.
 
 We work long, hard, in our own free time at developing and improving Courseplay. If you like the project, show us your undying love:
 
-[![paypal](https://www.paypalobjects.com/en_US/i/btn/btn_donateCC_LG.gif)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=7PDM2P6HQ5D56&item_name=Promote+the+development+of+Courseplay&currency_code=EUR&source=url)
+[![paypal](https://www.paypalobjects.com/en_US/i/btn/btn_donateCC_LG.gif)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=7PDM2P6HQ5D56&item_name=Promote+the+development+of+Courseplay&currency_code=EUR&source=url)
+
+<a href="https://www.buymeacoffee.com/courseplay" 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>