doc: add bdage of Github Release

Author: X1aomu

README.md

@@ -1,6 +1,7 @@
 # `zeus::expected`
 
 [![Tests Workflow](https://github.com/zeus-cpp/expected/actions/workflows/tests.yml/badge.svg?branch=main)](https://github.com/zeus-cpp/expected/actions/workflows/tests.yml?query=branch%3Amain)
+[![GitHub Release](https://img.shields.io/github/v/release/zeus-cpp/expected?color=green)](https://github.com/zeus-cpp/expected/releases)
 [![Conan Center](https://img.shields.io/conan/v/zeus_expected)](https://conan.io/center/recipes/zeus_expected)
 
 Backporting `std::expected` to C++17.