Add docs badge to README

Author: GabrielMajeri

README.md

@@ -1,6 +1,7 @@
 # uefi-rs
 
 [![Crates.io](https://img.shields.io/crates/v/uefi)](https://crates.io/crates/uefi)
+[![Docs.rs](https://docs.rs/uefi/badge.svg)](https://docs.rs/uefi)
 ![Stars](https://img.shields.io/github/stars/rust-osdev/uefi-rs)
 ![License](https://img.shields.io/github/license/rust-osdev/uefi-rs)
 [![Build Status](https://travis-ci.org/rust-osdev/uefi-rs.svg?branch=master)](https://travis-ci.org/rust-osdev/uefi-rs)