--format doc updated

Added the --format option was added to the intro.rst
These examples should be indented 4 spaces, not 2, in order to be properly rendered.

It may seem self-explanatory but it would likely be helpful to some if you created a table below this:

```rst
+--------------+---------------------+
| **Variable** | **Significance**    |
+--------------+---------------------+
| ``path``     | The file name       |
+--------------+---------------------+

.. etc.
```

You should probably look up the proper way to make a table in reStructuredText though since I haven't done it in a while.