add, or generate, shell completions

[merv4]

ykman(1) is a multilayered and verbose command. This allows for greater clarity and functionality, but can really hamper the user-experience - especially when using the OATH subcommand.

Shell completions for bash, fish, and zsh would make using this command a better/faster experience.

[dainnilsson]

Instructions for enabling shell completions are near the bottom of the README: https://github.com/Yubico/yubikey-manager?tab=readme-ov-file#shell-completion

[merv4]

Thanks for the correction and source, I missed it and will make sure to be more careful next time.

Is it possible to add the steps-for-activation to the manual itself? Probably under an "Experimental" header.