added documentation for manual count

Author: l3pp4rd

Diff for: Resources/doc/manual_counting.md

@@ -0,0 +1,32 @@
+# Manual counting
+
+**Note:** this documentation conserns more advanced usage of ORM
+query pagination. Paginator cannot support two **FROM** components
+or composite identifiers, because it cannot predict the total count
+in the database.
+
+The solution to that is simple and direct, you can provide the **count**
+manually through the hint on the query.
+
+## Usage example
+
+``` php
+<?php
+
+$paginator = new Paginator;
+
+$count = $entityManager
+    ->createQuery('SELECT COUNT(c) FROM Entity\CompositeKey c')
+    ->getSingleScalarResult()
+;
+
+$query = $entityManager
+    ->createQuery('SELECT c FROM Entity\CompositeKey c')
+    ->setHint('knp_paginator.count', $count)
+;
+$pagination = $paginator->paginate($query, 1, 10, array('distinct' => false));
+```
+
+Distinction in this case also cannot be determined by paginator. It will take direct result
+of the query and limit with offset. In some cases you may need to use **GROUP BY**
+