Docs: update Cookbook

Author: keradus

doc/COOKBOOK-FIXERS.md

@@ -76,6 +76,15 @@ final class RemoveCommentsFixer extends AbstractFixer
         // Return a definition of the fixer, it will be used in the README.rst.
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function isCandidate(Tokens $tokens)
+    {
+        // Check whether the collection is a candidate for fixing.
+        // Has to be ultra cheap to execute.
+    }
+
     /**
      * {@inheritdoc}
      */