[MERGE] Add user doc for stacked branches

[Scott Scriven]

* Ian Clatworthy <ian.clatworthy at canonical.com> wrote:
> +Pushing a stacked branch
> ...
> +  bzr push --stacked-url reference-url new-url
> +
> +This creates a new branch at ``my-url`` that is stacked on ``reference-url``

Small typo...  it looks like 'new-url' should be 'my-url'.


-- Scott