doc: Add `diffpy.morph` documentation to "products"

[cadenmyers13]

Problem

Diffpy.morph is not exposed to users when you visit diffpy.org. We need to add it.

Solution

We need to copy over or link the diffpy.morph docs. See #71 for how it was accomplished using diffpy.utils.

[sbillinge]

we don't copy over any docs. We just need diffpy.morph to appear as a product, lightweight instructions for who might use it and what they might use it for, then a link to the docs for that packages. Even installation instructions we would rather link to a central place (docs or readme) where this is described.

The main goal for all the packages is a more standardized and uniform diffpy.org page that takes minimal maintenance.

[cadenmyers13]

closing via #71