Increased the reserved memory from 10k to 32k

The ErrorHandler's job includes handling out of memory (OOM) exceptions,
therefore it is imoprtant that that feature works. In the current state,
when handling OOM exceptions, the error handler produces an OOM error
itself, because the old 10k reserve is apparently not enough anymore.
To mitigate that, the reserved memory gets bumped to 32k (which is enouogh).

ErrorHandler.php

@@ -119,7 +119,7 @@ class ErrorHandler
     public static function register(self $handler = null, $replace = true)
     {
         if (null === self::$reservedMemory) {
-            self::$reservedMemory = str_repeat('x', 10240);
+            self::$reservedMemory = str_repeat('x', 32768);
             register_shutdown_function(__CLASS__.'::handleFatalError');
         }
 

README.md

@@ -12,7 +12,7 @@ Getting Started
 ---------------
 
 ```
-$ composer install symfony/debug
+$ composer require symfony/debug
 ```
 
 ```php