Added note about caching a QueryResult (#5143)

Author: derhansen

Documentation/ExtensionArchitecture/Extbase/Reference/Domain/Repository.rst

@@ -58,6 +58,11 @@ Example:
 
     $this->blogRepository->findBy(['author' => 1, 'published' => true]);
 
+..  attention::
+    Saving a :php:`QueryResult` to a cache is not possible, if objects in the 
+    :php:`QueryResult` contain closures. This is typically the case for models
+    which use lazy loading on properties.
+
 ..  _extbase-repository-find-by-custom:
 
 Custom find methods