Add some more shields (#34)

README.md

@@ -2,6 +2,11 @@ Planus – alternative flatbuffer implementation
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 [![Build Status](https://github.com/TethysSvensson/planus/actions/workflows/rust.yml/badge.svg?branch=main)](https://github.com/TethysSvensson/planus/actions/workflows/rust.yml)
+![Rustc Version 1.57+](https://img.shields.io/badge/rustc-1.57+-lightgray.svg)
+[![License](https://img.shields.io/crates/l/planus)](https://crates.io/crates/planus)
+[![Crates.io](https://img.shields.io/crates/v/planus)](https://crates.io/crates/planus)
+[![Rust Documentation](https://img.shields.io/badge/api-rustdoc-blue.svg)](https://docs.rs/planus)
+
 
 Planus is an alternative compiler for [flatbuffers](https://google.github.io/flatbuffers/), an efficient cross platform serialization library.