Update README about MOSART being obscelensent

README.rst

@@ -5,6 +5,18 @@ Model for Scale Adaptive River Transport
 The Model for Scale Adaptive River Transport, Mosart,
 is part of the Community Earth System Model.
 
+IMPORTANT NOTE: MOSART is Obsolescent!
+
+MOSART is part of CESM3, but is obsolescent.
+
+We do not have support for creating input datasets for MOSART and
+as such can NOT use MOSART for Paleo work.
+
+Longer term MOSART will be removed in future versions of CESM and the new model
+mizuRoute will be used for Paleo work as well as present day.
+It's also possible that external collaborators will support the use of MOSART
+for present day climate even as mizuRoute becomes the default model for CESM.
+
 See the CESM web site for documentation and information:
 
 http://www.cesm.ucar.edu