Add a small mercurial repository as a sub-directory of a larger one - how?

[Chris Green]

I have a small mercurial repository (a bin directory on a host called
odin) that I want to add in to my main 'keep all my configuration
files and scripts' repository.

The files from odin's bin directory will live at <root>/odin/bin in
the main repository, this will be a new sub-directory.

How do I add in this sub-directory and keep the history?

-- 
Chris Green