Add crates.io badge for gd32c1.

Author: qwandor

README.md

@@ -1,6 +1,7 @@
 # GD32 Peripheral Access Crates
 
 [![CI](https://github.com/gd32-rust/gd32-rs/workflows/CI/badge.svg?branch=main)](https://github.com/gd32-rust/gd32-rs)
+[![crates.io](https://img.shields.io/crates/v/gd32c1.svg?label=gd32c1)](https://crates.io/crates/gd32c1)
 [![crates.io](https://img.shields.io/crates/v/gd32e1.svg?label=gd32e1)](https://crates.io/crates/gd32e1)
 [![crates.io](https://img.shields.io/crates/v/gd32e2.svg?label=gd32e2)](https://crates.io/crates/gd32e2)
 [![crates.io](https://img.shields.io/crates/v/gd32e5.svg?label=gd32e5)](https://crates.io/crates/gd32e5)