* Adds a simple bash completion script
This works with any loading script named openapi-generator-cli.
That is, if you've installed via homebrew or created a script similar
to https://gist.github.com/jimschubert/ce241b0c78140e364f46914ef8ec4103
This script is relatively simple, relying on fallback to the recently
add "completion" command to the CLI project.
The script includes a possible extension to allow for per-language
options to autocomplete when the user is applying additional properties.
This work is currently commented out, as it may be simplified a bit in
the CLI first.
* Add launcher script and "install" instructions
