doc: use literal markup for "flat" layout for consistency

Author: him2him2

doc/en/explanation/goodpractices.rst

@@ -153,7 +153,7 @@ which are better explained in this excellent `blog post`_ by Ionel Cristian Măr
 .. seealso::
 
     :doc:`packaging:discussions/src-layout-vs-flat-layout`
-        The Python Packaging User Guide discusses the trade-offs between the ``src`` layout and flat layout.
+        The Python Packaging User Guide discusses the trade-offs between the ``src`` layout and ``flat`` layout.
 
 Tests as part of application code
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^