docs: update README for crates.io availability

Remove "not yet available" note and add crates.io version badge.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: GiggleLiu

README.md

@@ -1,5 +1,6 @@
 ![100-Problem-Reductions](docs/logo.svg)
 
+[![Crates.io](https://img.shields.io/crates/v/problemreductions)](https://crates.io/crates/problemreductions)
 [![CI](https://github.com/CodingThrust/problem-reductions/actions/workflows/ci.yml/badge.svg)](https://github.com/CodingThrust/problem-reductions/actions/workflows/ci.yml)
 [![codecov](https://codecov.io/github/CodingThrust/problem-reductions/graph/badge.svg?token=0CdEC8GHN0)](https://codecov.io/github/CodingThrust/problem-reductions)
 [![Docs](https://img.shields.io/badge/Docs-API-green)](https://codingthrust.github.io/problem-reductions/)
@@ -10,7 +11,7 @@ A Rust library for NP-hard problem definitions and reductions. We aim to impleme
 
 ## Installation
 
-Add to your `Cargo.toml` (not yet available):
+Add to your `Cargo.toml`:
 
 ```toml
 [dependencies]