Add a badge for 0.1.0

README.md

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 RISC-V Supervisor Binary Interface implementation in Rust; runs on M-mode.
 
+[![crates.io](https://img.shields.io/crates/d/rustsbi.svg)](https://crates.io/crates/rustsbi)
+
 ## Binary downloads
 
 See [releases](https://github.com/luojia65/rustsbi/releases).