docs: update readme file (#15)

closes #7

Author: jmosawy

README.md

@@ -6,3 +6,21 @@ An opinionated and re-usable Prettier config file created by Jeff Mosawy
 [![version](https://img.shields.io/github/package-json/v/jmosawy/prettier-config)](https://github.com/jmosawy/prettier-config/)
 [![outdated](https://img.shields.io/librariesio/release/npm/@jmosawy/prettier-config)](https://github.com/jmosawy/prettier-config/)
 [![publish](https://github.com/jmosawy/prettier-config/actions/workflows/publish.yml/badge.svg)](https://github.com/jmosawy/)
+
+## Installation and usage
+
+> You most probably are familiar with Prettier, but in case you're not, visit their [website](https://prettier.io/) to learn more.
+
+To install this package, copy the following command into the terminal:
+
+```bash
+npm i @jmosawy/prettier-config -D
+```
+
+Then, create a prettier config file in your project's root, e.g. `.prettierrc`, and paste the following code:
+
+```
+"@jmosawy/prettier-config"
+```
+
+If you want to overwrite a config, please follow the instructions [here](https://prettier.io/docs/en/configuration.html#sharing-configurations).