add to docs

docs/src/IceNucleationParcel0D.md

@@ -245,10 +245,13 @@ Between each run the water vapor specific humidity is changed,
   of the previous run.
 The prescribed vertical velocity is equal to 3.5 cm/s.
 Supersaturation is plotted for both liquid (solid lines) and ice (dashed lines).
-The pale blue line uses the ``"MohlerRate_Deposition"``approach. When we force
+The pale blue line uses the ``"MohlerRate_Deposition"``approach. 
+  We only run it for the first GCM timestep because the rate approach requires
+  the change in ice saturation over time. With the discontinuous jump in saturation,
+  the parameterization is unablet to determine a proper nucleation rate. When we force
   the initial ice crystal number concentration for this simulation to match
   that in the ``"MohlerAF_Deposition"`` approach, we obtain the same results as
-  in the `"MohlerAF_Deposition"` approach.
+  in the `"MohlerAF_Deposition"` approach for the first GCM timestep.
 
 ```@example
 include("../../parcel/Tully_et_al_2023.jl")