Example to use babel generate instead of escodegen

[balazsnemeth]

The readme mention that the lib can be user with babel generate, but @babel/generator generate method requires the source as a text as input as far as I see.

Can you please give me some hint or an example how can I use babel generator with lave?

[balazsnemeth]

@jed , can you help on this maybe? If you give me a hint, probably I can create the example and submit it as a PR for adjusting readme.