Document how to opt-out of replacing files when loading a PCK file

This feature was added in Godot 3.2.

getting_started/workflow/export/exporting_pcks.rst

@@ -114,12 +114,15 @@ file in the directory of the games executable. The PCK file contains a
 
 .. warning::
 
-    If you import a file with the same file path/name as one you already have in your
+    By default, if you import a file with the same file path/name as one you already have in your
     project, the imported one will replace it. This is something to watch out for when
     creating DLC or mods (solved easily with a tool isolating mods to a specific mods
     subfolder). However, it is also a way of creating patches for one's own game. A
     PCK file of this kind can fix the content of a previously loaded PCK.
 
+    To opt out of this behavior, pass ``false`` as the second argument to
+    :ref:`ProjectSettings.load_resource_pack() <class_ProjectSettings_method_load_resource_pack>`.
+
 .. note::
     For a C# project, you need to build the DLL and place it in the project directory first.
     Then, before loading the resource pack, you need to load its DLL as follows: