Unexpected Completion Behavior

Consider the following simple example (from the docs)

```
#!/usr/bin/env python

import fire

def add(x, y):
return x + y

if __name__ == '__main__':
fire.Fire(add, name='./add.py')
```

The first command completion shows `add` and the second immediately `--x --y`.

This is confusing, since I would expect to see `X` and after I entered the first number I would expect `Y` or or even `X Y` at the very beginning so I know I have to enter 2 numbers, especially since the Usage shows

```
Usage: ./add.py X Y
./add.py --x X --y Y
```

As far as I can see it is also not possible to distinguish mandatory from optional arguments. In the case above `X` and `Y`are mandatory and I would not expect to see `--x`and `--y`. An optional argument could e.g. be `--modulo`, which would have a default value if not used, but how to distinguish that in the Python code from the other arguments?