Create example_ruleset.md

docs/example_ruleset.md

@@ -0,0 +1,27 @@
+```php
+<?php
+
+use Realodix\Relax\RuleSet\AbstractRuleSet;
+
+class MyRuleSet extends AbstractRuleSet
+{
+    // This method is optional. If not implemented, Relax will use
+    // the class name itself as the ruleset name.
+    public function name(): string
+    {
+        // ...
+    }
+
+    /**
+     * PHP-CS-Fixer rules
+     */
+    public function rules(): array
+    {
+        return [
+            '@PSR12' => true,
+            'array_syntax' => ['syntax' => 'short'],
+            // ...
+        ];
+    }
+}
+```