Add badges from crates.io to README

Author: zakcutner

README.md

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 # sliceslice
 
 [![Actions](https://github.com/marmeladema/sliceslice-rs/workflows/Check/badge.svg)](https://github.com/marmeladema/sliceslice-rs/actions)
+[![Crate](https://img.shields.io/crates/v/sliceslice)](https://crates.io/crates/sliceslice)
+[![Docs](https://docs.rs/mio/badge.svg)](https://docs.rs/sliceslice)
+[![License](https://img.shields.io/crates/l/sliceslice)](LICENSE)
 
 A fast implementation of single-pattern substring search using SIMD acceleration, based on the work [presented by Wojciech Muła](http://0x80.pl/articles/simd-strfind.html). For a fast multi-pattern substring search algorithm, see instead the [`aho-corasick` crate](https://github.com/BurntSushi/aho-corasick).