Document the expectations of two arguments.

To work with the updater, these files must have a certain prefix.

Test: Run with --help and upgrade a crate.
Change-Id: Icdc492479223865c39d6c6f10b84fe3d762f5d1d
diff --git a/scripts/cargo2android.py b/scripts/cargo2android.py
index 7abf897..fdd5188 100755
--- a/scripts/cargo2android.py
+++ b/scripts/cargo2android.py
@@ -1749,11 +1749,13 @@
   parser.add_argument(
       '--add-toplevel-block',
       type=str,
-      help='Add the contents of the given file to the top level of the Android.bp.')
+      help=('Add the contents of the given file to the top level of the Android.bp. ' +
+            'The filename should start with cargo2android to work with the updater.'))
   parser.add_argument(
       '--add-module-block',
       type=str,
-      help='Add the contents of the given file to the main module.')
+      help=('Add the contents of the given file to the main module. '+
+            'The filename should start with cargo2android to work with the updater.'))
   parser.add_argument(
       '--verbose',
       action='store_true',