Update to the command line help-prompt. Make filename non-optional.

pyrasite/main.py

@@ -27,7 +27,7 @@ def main():
         epilog="For updates, visit https://github.com/lmacken/pyrasite"
         )
     parser.add_argument('pid', help="The ID of the process to inject code into")
-    parser.add_argument('filename', default=None, nargs='?',
+    parser.add_argument('filename',
                         help="The second argument must be a filename")
     parser.add_argument('--gdb-prefix', dest='gdb_prefix',
                         help='GDB prefix (if specified during installation)',