        Change the dependencies of a TopGit-controlled topic branch.
        This should have several subcommands, but only `add` is
        supported right now.

        The `add` subcommand takes an argument naming a topic branch to
        be added, adds it to `.topdeps`, performs a commit and then
        updates your topic branch accordingly.  If you want to do other
        things related to the dependency addition, like adjusting
        `.topmsg`, use the option `--no-commit`.  Adding the
        `--no-update` (or `--no-commit`) option will suppress the
        `tg update` normally performed after committing the change.

        It is safe to run `tg depend add` in a dirty worktree, but the
        normally performed `tg update` will be suppressed in that case
        (even if neither `--no-update` nor `--no-commit` is given).

        You have enabled `git rerere` haven't you?

        | TODO: Subcommand for removing dependencies, obviously

