[Enhancement] - Better docs

[well-it-wasnt-me]

Would be nice to have in the readthedocs a full walk through.

How to use in the code

@app.command("/start")
async def handle_some_command(ack, body, logger):
    await ack()
    logger.info(body)

and the fact that you have to import from slack_bolt import App otherwise the suggestion in the terminal will give error

this project is very good, lacks only in proper documentation. If you can, please, update it (i would gladly do it...but i cant, really)