:memo: Explain how to embed a game

README.md

@@ -103,6 +103,23 @@ By default, to prevent side-effects and overcharge your computer resources, Slid
 - [x] Start when enabled : when the current slide is focused, set the process mode of every child to `PROCESS_MODE_PAUSABLE` ; otherwise, do not alter the process mode
 - [ ] Keep when disabled : keep the process state when the slideshow starts or when the focus go to another slide ; otherwise, set process mode to every child to `PROCESS_MODE_DISABLED`
 
+#### Embed your game in a slide
+
+1. Merge the project folder of your game into your show folder (both contain `project.godot`)
+2. Merge properties of `project.godot`, like input maps, physics layers ...
+3. Add a *SubViewport* in your slide scene
+4. Instantiate a game scene as a child of the SubViewport
+5. Make the SubViewport a child of a *SubViewportContainer*
+
+![example embedding a game using a SubViewportContainer](godot/example/screenshots/slide-show-plugin-embed-game-subviewportcontainer.png)
+
+*Alternative of merging games* : If you have conflicts when you merge your games files, you'd rather prefer to keep it in its own subfolder of your SlideShow project. Keep in mind that you have to fix every string in scripts referencing a resource by its path! (You can mitigate this by referencing uuid of resources instead).
+
+*Alternative for SubViewportContainer* : This node is useful to pass inputs to your game ; if you want only to demonstrate a visual effect, you can use a viewport texture referencing the subviewport parent of your demo scene, for instance in a `Sprite2D` or a `TextureRect`.
+
+![example embedding a scene using a TextureRect](godot/example/screenshots/slide-show-plugin-embed-scene-sprite.png)
+![example embedding a scene using a Sprite](godot/example/screenshots/slide-show-plugin-embed-scene-texturerect.png)
+
 #### Export your slides
 
 The plugin leverages the [Godot Movie Maker](https://docs.godotengine.org/en/stable/tutorials/animation/creating_movies.html) to easily export every slides to png files.
@@ -125,6 +142,14 @@ The export automation is enabled with two toggles in the `Show` node, in the _Ex
 
 Note : the export settings are effective only when the Movie Maker mode is enabled.
 
+## Troubleshoot
+
+### I have a physics scene in a scaled slide, physics nodes changed size when appearing !
+
+Sorry, Godot override scale when using physics.
+
+To prevent the scale of your slide in the main scene to disturb your physics simulation, embed it into a subviewport. See the "embed your game" instruction above.
+
 ## License
 
 This plugin is free software licensed under the [MIT license](https://mit-license.org/), the same license used by the Godot engine itself.