Add richer `--help` text to the CLI

Summary

Click supports adding help text to command options, which we can use to document the base tap and target options (--state, --catalog, etc.).

Proposed benefits

• Simple but nice thing we can offer out-of-the-box for connectors leveraging with the SDK.
• Improved experience for users of taps and targets built with the SDK.

Proposal details

Use the help argument from click to document the options:

$ tap-example --help
Usage: tap-example [OPTIONS]

  Handle command line execution.

Options:
  --state TEXT    <help for state>
  --catalog TEXT  <help for catalog>
  --config TEXT   <help for config>
  --format TEXT   <help for format>
  --test          <help for test>
  --discover      <help for discover>
  --about         <help for about>
  --version       <help for version>
  --help          Show this message and exit.

Best reasons not to build

None AFAICT 😸

Similar to meltano#2716 (closed) for the Meltano CLI.