Added a hint about a possible cause for why no mime type guesser is be available

src/Symfony/Component/HttpFoundation/File/MimeType/MimeTypeGuesser.php

@@ -111,7 +111,7 @@ class MimeTypeGuesser implements MimeTypeGuesserInterface
         }
 
         if (!$this->guessers) {
-            throw new \LogicException('Unable to guess the mime type as no guessers are available.');
+            throw new \LogicException('Unable to guess the mime type as no guessers are available (Did you enable the php_fileinfo extension?)');
         }
 
         foreach ($this->guessers as $guesser) {