docs: add crypto donate badge to the project readme

Signed-off-by: Milad Nekofar <milad@nekofar.com>

README.md

@@ -9,6 +9,8 @@
 [![Coverage Status][icon-coverage]][link-coverage]
 [![License][icon-license]][link-license]
 [![Twitter: nekofar][icon-twitter]][link-twitter]
+[![Donate](https://img.shields.io/badge/donate-nekofar.crypto-a2b9bc?logo=ko-fi&logoColor=white)](https://ud.me/nekofar.crypto)
+
 
 [Omnipay](https://github.com/thephpleague/omnipay) is a framework agnostic, multi-gateway payment
 processing library for PHP. This package implements ZarinPal support for Omnipay.