Improved Doctrine docs [skip ci]

Author: ankane

README.md

@@ -139,6 +139,12 @@ $config->addCustomNumericFunction('hamming_distance', 'Pgvector\Doctrine\Hamming
 $config->addCustomNumericFunction('jaccard_distance', 'Pgvector\Doctrine\JaccardDistance');
 ```
 
+Enable the extension
+
+```php
+$entityManager->getConnection()->executeStatement('CREATE EXTENSION IF NOT EXISTS vector');
+```
+
 Update your model
 
 ```php

tests/DoctrineTest.php

@@ -38,6 +38,7 @@ public static function setUpBeforeClass(): void
         ], $config);
 
         $entityManager = new EntityManager($connection, $config);
+        $entityManager->getConnection()->executeStatement('CREATE EXTENSION IF NOT EXISTS vector');
 
         Type::addType('vector', 'Pgvector\Doctrine\VectorType');
         Type::addType('halfvec', 'Pgvector\Doctrine\HalfVectorType');