Fixed typo in [include] section example.

docs/configuration.rst

@@ -990,7 +990,7 @@ configuration.
 .. code-block:: ini
 
    [include]
-   file = /an/absolute/filename.conf /an/absolute/*.conf foo.conf config??.conf
+   files = /an/absolute/filename.conf /an/absolute/*.conf foo.conf config??.conf
 
 ``[group:x]`` Section Settings
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