[MsgPhpUserBundle] add post-install.txt

msgphp/user-bundle/0.3/config/packages/msgphp_user.php

@@ -0,0 +1,12 @@
+<?php
+
+use MsgPhp\User\Entity\User;
+use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+return function (ContainerConfigurator $container) {
+    $container->extension('msgphp_user', [
+        'class_mapping' => [
+            User::class => \App\Entity\User\User::class,
+        ],
+    ]);
+};