wrong link to Lithology docs

[speleophysics]

In the Lithology and LithoLayers tutorial the link to the full Litholayers documentation is incorrect. It points to layers.litholayers. I think it should be components.litholayers.

[kbarnhart]

@speleophysics thanks for catching that. Looks like some of the other links to the landlab docs are broken too. PR fixing those forthcoming.

This issue is associated with the JOSS review of this submodule.