docs(badges): add codecov status badge and installation instruction (#13

)

README.md

@@ -6,8 +6,9 @@
 </p>
 </div>
 
-![Crates.io (latest)](https://img.shields.io/crates/v/docstring-rs)
+[![Crates.io (latest)](https://img.shields.io/crates/v/docstring-rs)](https://crates.io/crates/docstring-rs)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+[![codecov](https://codecov.io/gh/wilhelmagren/docstring-rs/graph/badge.svg?token=DAOMDVU8QF)](https://codecov.io/gh/wilhelmagren/docstring-rs)
 [![CI](https://github.com/wilhelmagren/docstring-rs/actions/workflows/ci.yml/badge.svg)](https://github.com/wilhelmagren/docstring-rs/actions/workflows/ci.yml)
 [![Tests](https://github.com/wilhelmagren/docstring-rs/actions/workflows/tests.yml/badge.svg)](https://github.com/wilhelmagren/docstring-rs/actions/workflows/tests.yml)
 
@@ -18,6 +19,9 @@ Automatically generate new files with header docstring based on LICENSE informat
 
 ## 📦 Installation
 ...
+```
+cargo install docstring-rs
+```
 
 ## 🚀 Example usage
 ...