Add bitcoin donation button

README.md

@@ -3,6 +3,7 @@
 [![Go Report Card](https://goreportcard.com/badge/code.dumpstack.io/tools/out-of-tree)](https://goreportcard.com/report/code.dumpstack.io/tools/out-of-tree)
 [![Documentation Status](https://readthedocs.org/projects/out-of-tree/badge/?version=latest)](https://out-of-tree.readthedocs.io/en/latest/?badge=latest)
 [![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=R8W2UQPZ5X5JE&source=url)
+[![Donate](https://img.shields.io/badge/Donate-BitCoin-green.svg)](bitcoin:bc1q23fyuq7kmngrgqgp6yq9hk8a5q460f39m8nv87)
 
 # [out-of-tree](https://out-of-tree.io)