Recommend registering the error handler in prod

This is what currently happens when using Symfony in a standard way, and
people have been wondering online about alarming exceptions from the
Debug component in production.

See https://stackoverflow.com/questions/37431935/is-it-normal-to-have-symfony-component-debug-exception-fatalerrorexception-excep

Author: greg0ire

components/debug.rst

@@ -37,8 +37,9 @@ tools.
 
 .. caution::
 
-    You should never enable the debug tools in a production environment as
-    they might disclose sensitive information to the user.
+    Apart from the error handler, you should never enable the debug
+    tools in a production environment as they might disclose sensitive
+    information to the user.
 
 Enabling the Error Handler
 --------------------------
@@ -52,6 +53,12 @@ fatal errors)::
 
     ErrorHandler::register();
 
+.. note::
+
+    This one is fine to use in a production environment and will be
+    enabled if you use the framework bundle, so that you get better
+    logging.
+
 Enabling the Exception Handler
 ------------------------------