add a comment for Iris 26 incompat reason

versionProperties/26.1.0.properties

@@ -26,6 +26,9 @@ bclib_version=
 immersive_portals_version=
 canvas_version=
 
+# There is a bug on Iris' end where it fails to rebind "sampler1"
+# causing a Blaze3D validation to fail, crashing the renderer.
+# Unfortunately this bug doesn't appear to be fixable on DH's end.
 fabric_incompatibility_list={ "iris": "*" }
 fabric_recommend_list={}