minor #1132 Link to Monolog provider chapter (SpacePossum)

This PR was submitted for the 1.3 branch but it was merged into the 1.2 branch instead (closes #1132).

Discussion
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Link to Monolog provider chapter

Commits
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e4907268 Link to Monolog provider chapter

doc/usage.rst

@@ -535,7 +535,7 @@ once a response is returned, the following handlers are ignored.
 .. note::
 
     Silex ships with a provider for Monolog_ which handles logging of errors.
-    Check out the *Providers* chapter for details.
+    Check out the *Providers* :doc:`chapter <providers/monolog>` for details.
 
 .. tip::