minor #10668 Recommend registering the error handler in prod (greg0ire)

This PR was submitted for the 2.8 branch but it was merged into the 3.4 branch instead (closes #10668).

Discussion
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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

Commits
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f0cd0bf Recommend registering the error handler in prod

Author: javiereguiluz

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
 ------------------------------