xz doc patch posted for review

[Bruno Wolff III]

The proposed documentation patch is attached.

There will be another revision when (and if) the default changes. But this
is the fall back for xz being available, even if we decide not to use it
by default for spin creation.

[Brian C. Lane]

On Sat, Jan 15, 2011 at 11:16:51PM -0600, Bruno Wolff III wrote:
> The proposed documentation patch is attached.

Looks good to me.