[feature] Shell completions

[Freed-Wu]

Like

• https://github.com/andreafrancia/trash-cli/blob/master/setup.cfg#L31-L33
• https://github.com/inducer/pudb/blob/main/setup.py#L28
• https://github.com/piccolomo/plotext/blob/master/setup.py#L25
• https://github.com/wookayin/gpustat/blob/master/setup.py#L114

TIA!

[jaraco]

Sounds good. Would someone be interested in helping implement these?