minor #7588 Added a link to Composer's loader optimizations (javiereguiluz)

This PR was merged into the master branch.

Discussion
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Added a link to Composer's loader optimizations

This fixes #7533.

Commits
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3138745 Added a link to Composer's loader optimizations

Author: wouterj

components/class_loader.rst

@@ -10,7 +10,8 @@ The ClassLoader Component
 .. caution::
 
     The ClassLoader component was deprecated in Symfony 3.3 and it will be
-    removed in 4.0. As an alternative, use Composer's class loading mechanism.
+    removed in 4.0. As an alternative, use any of the `class loading optimizations`_
+    provided by Composer.
 
 Usage
 -----
@@ -71,3 +72,4 @@ Learn More
 .. _PSR-4: http://www.php-fig.org/psr/psr-4/
 .. _`autoloading mechanism`: http://php.net/manual/en/language.oop5.autoload.php
 .. _Packagist: https://packagist.org/packages/symfony/class-loader
+.. _`class loading optimizations`: https://getcomposer.org/doc/articles/autoloader-optimization.md