Get a list of all valid commands when writing --help

Thanks for creating this amazing library. I'm somewhat confused as to how the `--help` command is implemented. When running `python example.py --help` Fire only prints the flags, not the actual commands that can be run (see example below):

```
NAME
fury.py

SYNOPSIS
fury.py

FLAGS
--verbosity=VERBOSITY
```

How do I make `--help` show all the possible commands and why is that not the default? :)