Add qiime2 karenina tutorial documentation to q2-karenina

[zaneveld]

Per e-mail discussion with Greg, it's totally fine to add our QIIME2 tutorial under version control in the q2-karenina project, and then just post a brief description of what the module does to the qiime community forum.

This is vastly preferable IMO because it allows us to update the tutorial to add new capabilites, etc. It also is more discoverable to users that come to the GitHub page from somewhere other than QIIME2.

[zaneveld]

One issue we'll want to address here and in karenina:
it's unsustainable and error-prone to have to manually edit Sphinx output to remove underscored directories. I think the solution by suhailvs on this thread appears to be a workable solution: sphinx-doc/sphinx#3382