Added walle, a Bitcoin wallet written in Zig (#86)

Author: iskyd

README.md

@@ -546,6 +546,7 @@ TOC is generated by [markdown-toc](https://github.com/jonschlinkert/markdown-toc
 - [jsign/verkle-crypto](https://github.com/jsign/verkle-crypto) : Cryptography for Ethereum Verkle Trees.
 - [Ultra-Code/recblock](https://github.com/Ultra-Code/recblock) : Blockchain for a record management and money transfer system.
 - [keep-starknet-strange/ziggy-starkdust](https://github.com/keep-starknet-strange/ziggy-starkdust) : A Zig implementation of Cairo VM for Cairo, the STARK powered provable language.
+- [iskyd/walle](https://github.com/iskyd/walle) : A Bitcoin Wallet written in Zig.
 
 ## WebAssembly