improve help msg for mk_prepare_receptor --write flags

scripts/mk_prepare_receptor.py

@@ -935,9 +935,16 @@ def warn_flexres_outside_box(chorizo, box_center, box_size):
         print(line % (fn, desc))
 else:
     print()
-    print("You have successfully prepared the receptor, but no files were written.")
-    print("Likely, you want to use some of the --write options, for example:")
-    print("  -p/--write_pdbqt, -j/--write_json, -g/--write_gpf, -v/--write_vina_box")
+    print()
+    print("Receptor was prepared, but no files were written.")
+    print("")
+    print("Consider the following --write options:")
+    print("  -p/--write_pdbqt")
+    print("  -j/--write_json")
+    print("  -g/--write_gpf")
+    print("  -v/--write_vina_box")
+    print("")
+    print("Use -o/--output_basename, or set a filename after each --write flag")
     print("")
     print("Recommended for AutoDock-GPU:")
     print("  -o my_receptor -p -j -g")