Document how to avoid light leaks with GIProbe and SDFGI

doc/classes/Environment.xml

@@ -176,6 +176,8 @@
 		<member name="sdfgi_cascades" type="int" setter="set_sdfgi_cascades" getter="get_sdfgi_cascades" enum="Environment.SDFGICascades" default="1">
 		</member>
 		<member name="sdfgi_enabled" type="bool" setter="set_sdfgi_enabled" getter="is_sdfgi_enabled" default="false">
+			If [code]true[/code], enables signed distance field global illumination.
+			[b]Note:[/b] Meshes should have sufficiently thick walls to avoid light leaks (avoid one-sided walls). For interior levels, enclose your level geometry in a sufficiently large box and bridge the loops to close the mesh.
 		</member>
 		<member name="sdfgi_energy" type="float" setter="set_sdfgi_energy" getter="get_sdfgi_energy" default="1.0">
 		</member>

doc/classes/GIProbe.xml

@@ -6,6 +6,7 @@
 	<description>
 		[GIProbe]s are used to provide high-quality real-time indirect light to scenes. They precompute the effect of objects that emit light and the effect of static geometry to simulate the behavior of complex light in real-time. [GIProbe]s need to be baked before using, however, once baked, dynamic objects will receive light from them. Further, lights can be fully dynamic or baked.
 		Having [GIProbe]s in a scene can be expensive, the quality of the probe can be turned down in exchange for better performance in the [ProjectSettings] using [member ProjectSettings.rendering/global_illumination/gi_probes/quality].
+		[b]Note:[/b] Meshes should have sufficiently thick walls to avoid light leaks (avoid one-sided walls). For interior levels, enclose your level geometry in a sufficiently large box and bridge the loops to close the mesh.
 	</description>
 	<tutorials>
 		<link title="GI probes">https://docs.godotengine.org/en/latest/tutorials/3d/gi_probes.html</link>