docopt badge on structopt-derive in README.md
-# StructOpt [![Build status](https://travis-ci.org/TeXitoi/structopt.svg?branch=master)](https://travis-ci.org/TeXitoi/structopt) [![](https://img.shields.io/crates/v/structopt.svg)](https://crates.io/crates/structopt) [![](https://docs.rs/structopt/badge.svg)](https://docs.rs/structopt-derive)
+# StructOpt [![Build status](https://travis-ci.org/TeXitoi/structopt.svg?branch=master)](https://travis-ci.org/TeXitoi/structopt) [![](https://img.shields.io/crates/v/structopt.svg)](https://crates.io/crates/structopt) [![](https://docs.rs/structopt-derive/badge.svg)](https://docs.rs/structopt-derive)
Parse command line argument by defining a struct. It combines [clap](https://crates.io/crates/clap) with custom derive.
