update usage message evolven3fit to mention changed syntax

n3fit/src/n3fit/scripts/evolven3fit.py

@@ -95,7 +95,16 @@ def evolven3fit_new():
 
 
 def main():
-    parser = ArgumentParser(description="evolven3fit - a script with tools to evolve PDF fits")
+    parser = ArgumentParser(
+        description="evolven3fit - a script with tools to evolve PDF fits",
+        usage="""evolven3fit [-h] [-q Q_FIN] [-p Q_POINTS] [-n N_CORES] [-e EV_OP_ITERATIONS] [--use-fhmruvv]
+        {produce_eko,produce_eko_photon,evolve} [fit folder]
+
+        Note that with the now removed apfel-based version of `evolven3fit` the syntax was
+        `evolven3fit [fit folder] [number of replicas]`. This syntax is no longer supported in the
+        eko-based version of evolven3fit.
+        """,
+    )
     parser.add_argument(
         "-q", "--q-fin", type=float, default=None, help="Final q-value of the evolution"
     )
@@ -121,6 +130,7 @@ def main():
     construct_evolven3fit_parser(subparsers)
 
     args = parser.parse_args()
+
     op_card_info = {
         "configs": {"n_integration_cores": args.n_cores, "ev_op_iterations": args.ev_op_iterations}
     }