Add boilerplate code, Docker environment, Makefile etc.

tests/Unit/HelloWorldTest.php

@@ -0,0 +1,18 @@
+<?php
+declare(strict_types=1);
+
+namespace Tests\Unit;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @coversNothing
+ */
+final class HelloWorldTest extends TestCase
+{
+    // TODO: Delete this file
+    public function testTrue(): void
+    {
+        $this->assertTrue(true);
+    }
+}