docs: add sponsor badge

Author: The Crypto Donkey

README.md

@@ -4,6 +4,7 @@
 
 [![npm](https://img.shields.io/npm/v/@forgesworn/range-proof)](https://www.npmjs.com/package/@forgesworn/range-proof)
 [![CI](https://github.com/forgesworn/range-proof/actions/workflows/ci.yml/badge.svg)](https://github.com/forgesworn/range-proof/actions/workflows/ci.yml)
+[![GitHub Sponsors](https://img.shields.io/github/sponsors/TheCryptoDonkey?logo=githubsponsors&color=ea4aaa&label=Sponsor)](https://github.com/sponsors/TheCryptoDonkey)
 
 Pedersen commitment range proofs on secp256k1.