Add render() Method

src/Potter/Renderable/AbstractRenderable.php

@@ -6,5 +6,5 @@ namespace Potter\Renderable;
 
 abstract class AbstractRenderable implements RenderableInterface
 {
-
+    abstract public function render(): string;
 }

src/Potter/Renderable/RenderableInterface.php

@@ -6,5 +6,5 @@ namespace Potter\Renderable;
 
 interface RenderableInterface 
 {
-
+     public function render(): string;
 }

src/Potter/Renderable/RenderableTrait.php

@@ -6,5 +6,5 @@ namespace Potter\Renderable;
 
 trait RenderableTrait 
 {
-
+    abstract public function render(): string;
 }