[MERGE][1.14][trivial] Fix development-rich-root's help string

[Aaron Bentley]

Aaron Bentley has voted approve.
Status is now: Approved
Comment:
The statement "Can convert data to and from rich-root-pack (and anything 
compatible with rich-root-pack) format repositories" is a bit imprecise 
because arguably, development-subtree is compatible with rich-root-pack.

Still an improvement.  I'll merge.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C49DB6C4F.5070408%40mattnordhoff.com%3E
Project: Bazaar