Update _index.md about switching container mode (#21614)

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## Description

<!-- Tell us what you did and why -->
Docker desktop was installed by an automated system on my device and
when I went to change the WSL Integration settings, the panel was not
available. The app had been configured to use "Windows containers mode"
and I had to switch it to "Linux containers mode" to be able to see the
panel. I have added text to help others who may face the same problem.

## Related issues or tickets

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## Reviews

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- [ ] Technical review
- [ ] Editorial review
- [ ] Product review

---------

Co-authored-by: Allie Sadler <[email protected]>

Author: radiant-tangent

content/manuals/desktop/features/wsl/_index.md

@@ -90,6 +90,7 @@ Docker Desktop does not require any particular Linux distributions to be install
      ```console
     $ wsl --set-default <distribution name>
     ```
+   If **WSL integrations** isn't available under **Resources**, Docker may be in Windows container mode. In your taskbar, select the Docker menu and then **Switch to Linux containers**.
 
 3. Select **Apply & Restart**.