Update docs; resolve #6623 (#6693)

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## 📝 Summary

Clarified guide page [**"Run as an
app"**](https://docs.marimo.io/guides/apps/#layout) to resolve #6623

## Description

- Moved note about `layouts/` folder from `### Grid layout` to `##
Layout`, since it applies to both Grid and Slides layouts.
- Added instruction to include `layouts/` folder in version control.

## 📋 Checklist

- [x] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [x] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on
[Discord](https://marimo.io/discord?ref=pr), or the community
[discussions](https://github.com/marimo-team/marimo/discussions) (Please
provide a link if applicable).
- [x] I have added tests for the changes made.
- [x] I have run the code and verified that it works as expected.

Author: stephenlf

docs/guides/apps.md

@@ -23,6 +23,12 @@ While editing a notebook with `marimo edit`, you can preview the notebook
 as an app by clicking the preview button in the bottom-right of the editor.
 (You can also use the command palette.)
 
+!!! note "`layouts` folder"
+   marimo saves metadata about your constructed layout in a `layouts` folder;
+   make sure to include this folder when sharing or deploying your notebook
+   so that others can reconstruct your layout. Include this folder in version
+   control.
+
 ### Vertical layout
 
 The default layout is the vertical layout: cell outputs are concatenated
@@ -53,10 +59,6 @@ Enable the grid editor in the app preview, via a dropdown:
   <figcaption>Grid layout lets you drag and drop outputs to construct your app</figcaption>
 </div>
 
-marimo saves metadata about your constructed layout in a `layouts` folder;
-make sure to include this folder when sharing your notebook so that others
-can reconstruct your layout.
-
 ### Slides layout
 
 If you prefer a slideshow-like experience, you can use the slides layout. Enable the slides layout in the app preview, via the same dropdown as above.