Fix some errors in Environment documentation

Co-authored-by: Clay John <[email protected]>
Co-authored-by: Max Hilbrunner <[email protected]>
Co-authored-by: Rémi Verschelde <[email protected]>
(cherry picked from commit 0af26280b6a2dc24501be56615b89cff1d602da1)

doc/classes/Environment.xml

@@ -9,7 +9,11 @@
 		- Glow
 		- Tonemap (Auto Exposure)
 		- Adjustments
-		These effects will only apply when the [Viewport]'s intended usage is "3D" or "3D Without Effects". This can be configured for the root Viewport with [member ProjectSettings.rendering/quality/intended_usage/framebuffer_allocation], or for specific Viewports via the [member Viewport.usage] property.
+		If the target [Viewport] is set to "2D Without Sampling", all post-processing effects will be unavailable. With "3D Without Effects", the following options will be unavailable:
+		- Ssao
+		- Ss Reflections
+		This can be configured for the root Viewport with [member ProjectSettings.rendering/quality/intended_usage/framebuffer_allocation], or for specific Viewports via the [member Viewport.usage] property.
+		Note that [member ProjectSettings.rendering/quality/intended_usage/framebuffer_allocation] has a mobile platform override to use "3D Without Effects" by default. It improves the performance on mobile devices, but at the same time affects the screen display on mobile devices.
 	</description>
 	<tutorials>
 		<link title="Environment and post-processing">https://docs.godotengine.org/en/3.4/tutorials/3d/environment_and_post_processing.html</link>