Better rendering for a single command with lots of subcommands

[tsibley]

A common CLI pattern is to have a single top-level command with lots of subcommands (e.g. git, docker). Currently that renders a heading/TOC tree like this (using git as an example):

git
  Sub-commands:
    init
    clone
    checkout
    …

This adds what feels like an unnecessary level of nesting due to the presence of the Sub-commands heading. It would be nice to be able to suppress this, at least for the top-level command/parser, e.g.:

git
  init
  clone
  checkout
  …

or even flatten/splat them entirely as:

init
clone
checkout
…

without having to give up auto-generation of subcommands and explicitly name init, clone, checkout, … in the RST document.