docs(prt-fmi): clarify only required when post-processing

autotest/test_prt_exg.py

@@ -108,15 +108,17 @@ def build_mf6_sim(idx, test):
         trackcsv_filerecord=[prt_track_csv_file],
     )
 
-    # create a flow model interface
-    # todo Mike Fienen's report (crash when FMI created but not needed)
-    # flopy.mf6.ModflowPrtfmi(
-    #     prt,
-    #     packagedata=[
-    #         ("GWFHEAD", gwf_head_file),
-    #         ("GWFBUDGET", gwf_budget_file),
-    #     ],
-    # )
+    # create a flow model interface. should be ignored.
+    # Mike Fienen reported that an early version of PRT
+    # crashed if an FMI provided when using an exchange.
+    flopy.mf6.ModflowPrtfmi(
+        prt,
+        packagedata=[
+            # garbage paths
+            ("GWFHEAD", "heads.hds"),
+            ("GWFBUDGET", "budget.cbc"),
+        ],
+    )
 
     # create exchange
     gwf_name = get_model_name(idx, "gwf")

doc/mf6io/prt/fmi.tex

@@ -1,6 +1,6 @@
-Flow Model Interface (FMI) Package information is read from the file that is specified by ``FMI6'' as the file type.  The FMI Package is required, and only one FMI Package can be specified for a PRT model.
+Flow Model Interface (FMI) Package information is read from the file that is specified by ``FMI6'' as the file type.  The FMI Package is required if the PRT Model is not running in the same simulation as the flow model. Only one FMI Package can be specified for a PRT model.
 
-For most simulations, the PRT Model needs groundwater flows for every cell in the model grid, for all boundary conditions, and for other terms, such as the flow of water in or out of storage.  The FMI Package is the interface between the PRT Model and simulated groundwater flows provided by a corresponding GWF Model that is running concurrently within the simulation or from binary budget files that were created from a previous GWF model run.  The following are several different FMI simulation cases:
+The PRT Model needs groundwater flows for model grid cells, for boundary conditions, and for other terms, such as the flow of water in or out of storage.  The FMI Package is the interface between the PRT Model and simulated groundwater flows provided by a corresponding GWF Model that is running concurrently within the simulation or from binary budget files that were created from a previous GWF model run.  The following are several different FMI simulation cases:
 
 \begin{itemize}