adds known issue for instanceable assets as markers

docs/source/refs/issues.rst

@@ -20,3 +20,17 @@ its pose:
     # note: the number of steps might vary depending on how complicated the scene is.
     for _ in range(12):
         sim.render()
+
+
+Using instanceable assets for markers
+-------------------------------------
+
+When using `instanceable assets`_ for markers, the markers do not work properly, since Omniverse does not support
+instanceable assets when using the :class:`UsdGeom.PointInstancer` schema. This is a known issue and will hopefully
+be fixed in a future release.
+
+If you use an instanceable assets for markers, the marker class removes all the physics properties of the asset.
+This is then replicated across other references of the same asset since physics properties of instanceable assets
+are stored in the instanceable asset's USD file and not in its stage reference's USD file.
+
+.. _instanceable assets: https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/tutorial_gym_instanceable_assets.html