Fixes double call to cell help command

[JasonWeill]

Fixes the %ai help command to only display the %%ai cell magic help information once, not twice. Updates sample notebook. Fixes #204.

Revised output is below.

Usage: %%ai [OPTIONS] MODEL_ID

  Invokes a language model identified by MODEL_ID, with the prompt being
  contained in all lines after the first. Both local model IDs and global
  model IDs (with the provider ID explicitly prefixed, followed by a colon)
  are accepted.

  To view available language models, please run `%ai list`.

Options:
  -f, --format [code|html|image|json|markdown|math|md|text]
                                  IPython display to use when rendering
                                  output. [default="markdown"]
  -r, --reset                     Clears the conversation transcript used when
                                  interacting with an OpenAI chat model
                                  provider. Does nothing with other providers.
  -n, --region-name TEXT          AWS region name, e.g. 'us-east-1'. Required
                                  for SageMaker provider; does nothing with
                                  other providers.
  -q, --request-schema TEXT       The JSON object the endpoint expects, with
                                  the prompt being substituted into any value
                                  that matches the string literal '<prompt>'.
                                  Required for SageMaker provider; does
                                  nothing with other providers.
  -p, --response-path TEXT        A JSONPath string that retrieves the
                                  language model's output from the endpoint's
                                  JSON response. Required for SageMaker
                                  provider; does nothing with other providers.
  --help                          Show this message and exit.
------------------------------------------------------------------------------
Usage: %ai [OPTIONS] COMMAND [ARGS]...

  Invokes a subcommand.

Options:
  --help  Show this message and exit.

Commands:
  delete    Delete an alias. See `%ai delete --help` for options.
  error     Explains the most recent error.
  help      Show this message and exit.
  list      List language models. See `%ai list --help` for options.
  register  Register a new alias. See `%ai register --help` for options.
  update    Update the target of an alias. See `%ai update --help` for
            options.