Re: [PATCH v3] worktree: clarify that --expire only affects missing worktrees

> The --expire option for "git worktree list" and "git worktree prune"
> only affects worktrees whose working directory path no longer exists.
> The help text did not make this clear, and the documentation
> inconsistently used "unused" for prune but "missing" for list.
>
> Update the help text and documentation to consistently describe these
> as "missing worktrees", and use "prune" instead of "expire" when
> describing the effect on missing worktrees since the terminology is
> clearer.
>
> While at it, expand the description of the "prune" subcommand itself
> to better explain what it does and when to use it, as suggested by
> Junio.
>
> Signed-off-by: Sam Bostock <sam@sambostock.ca>
> ---
>     Changes from v2:
>      * Squash into a single commit
>      * Expand the prune subcommand description per Junio's suggestion