Update index.rst

Fix getPropertyAnnotation second argument

Author: l-vo

docs/en/index.rst

@@ -73,7 +73,7 @@ annotations of a class. A common one is
     $property = $reflectionClass->getProperty('bar');
 
     $reader = new AnnotationReader();
-    $myAnnotation = $reader->getPropertyAnnotation($property, 'bar');
+    $myAnnotation = $reader->getPropertyAnnotation($property, MyAnnotation::class);
 
     echo $myAnnotation->myProperty; // result: "value"