Add header image to README

Add a branded header image to the README and exclude the /art directory from the distributed package via export-ignore in .gitattributes.

Author: codearachnid

.gitattributes

@@ -3,6 +3,7 @@
 
 # Exclude development-only files from the distributed package.
 /.github            export-ignore
+/art                export-ignore
 /tests              export-ignore
 /.editorconfig      export-ignore
 /.gitattributes     export-ignore

README.md

@@ -1,5 +1,7 @@
 # Laravel VIN
 
+![Laravel VIN — powerful VIN lookup for Laravel](art/header.png)
+
 [![Latest Version on Packagist](https://img.shields.io/packagist/v/alwayscurious/laravel-vin.svg?style=flat-square)](https://packagist.org/packages/alwayscurious/laravel-vin)
 [![Tests](https://github.com/alwayscurious/laravel-vin/actions/workflows/tests.yml/badge.svg)](https://github.com/alwayscurious/laravel-vin/actions/workflows/tests.yml)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg?style=flat-square)](LICENSE)