Update README

Added a backstory and some usage instructions to guide users.

Author: rdohms

README.md

@@ -0,0 +1,46 @@
+# PHPUnit AssertArraySubset Extension
+
+In PHPunit 8 the function `assertArraySubset` was [deprecated](https://github.com/sebastianbergmann/phpunit/issues/3494). This function was often misunderstood and this removed, but it still holds true as a very useful tool, hence it was extracted here.
+
+**Disclaimer**
+The initial version contained here is copied over from phpunit and is heavilybased on the original work by [Márcio Almada](https://github.com/marcioAlmada) 
+
+## Installation
+
+Simply use it by importing it with Composer
+
+```
+composer require dms/phpunit-arraysubset-asserts
+```
+
+## Usage
+
+You have two options to use this in your classes, either directly as a static call or as a trait if you with to keep existing references working.
+
+```php
+<?php
+declare(strict_types=1);
+
+namespace DMS\Tests;
+
+use DMS\PHPUnitExtensions\ArraySubset\Assert;
+use DMS\PHPUnitExtensions\ArraySubset\ArraySubsetAsserts;
+use PHPUnit\Framework\TestCase;
+
+
+final class AssertTest extends TestCase
+{
+    use ArraySubsetAsserts;
+    
+    public function testWithTrait(): void
+    {
+        self::assertArraySubset(['bar' => 0], ['bar' => '0'], true);
+    }
+
+    public function testWithDirectCall(): void
+    {
+        Assert::assertArraySubset(['bar' => 0], ['bar' => '0'], true);
+    }
+}
+
+```