docs: Add Mesa GPU selection and XWayland fallback instructions (#39930)

William Fleurant and Finn Evers created 

Related #35948

Should document it.. re:
- Added documentation for Mesa GPU device selection using environment
variables
- Added instructions for XWayland fallback when using Wayland


Release Notes:

- N/A

---------

Co-authored-by: Finn Evers <finn.evers@outlook.de>

Change summary

docs/src/linux.md | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Detailed changes

docs/src/linux.md 🔗 

@@ -179,7 +179,7 @@ Make sure to export the variable if you choose to define it globally in a `.bash
 
 ##### Option B
 
-If you are using Mesa, you can run `MESA_VK_DEVICE_SELECT=list zed --foreground` to get a list of available GPUs and then export `MESA_VK_DEVICE_SELECT=xxxx:yyyy` to choose a specific device.
+If you are using Mesa, you can run `MESA_VK_DEVICE_SELECT=list zed --foreground` to get a list of available GPUs and then export `MESA_VK_DEVICE_SELECT=xxxx:yyyy` to choose a specific device. Furthermore, you can fallback to xwayland with an additional export of `WAYLAND_DISPLAY=""`.
 
 ##### Option C