Remove source discovery tool README

[troyraen]

We may want to move the list of directory contents and related comments into the notebook to preserve them.

I thought about rendering this, but the overview and setup instructions are repeated in the notebook, so the only content in here that's not also in the notebook is the directory contents. So I opted not to render this README, and instead I just pointed the TOC and the spherex landing page directly to the notebook. That seemed better than creating another level in the hierarchy for this readme / landing page. Thoughts?

Originally posted by @troyraen in #258 (comment)

keeping it separate and outside of all the checks would make it rather vulnarable for bit-rot as well as subject to divergence from the content in the notebook.
Besides, if the content is being kept in the notebook, too, then there is no need for the duplicated file while if there are multiple notebooks in the future using the same instructions having the separate file would be nice, but then we should just link to it from the notebooks.

It's not urgent to address, but something to keep in mind.

Originally posted by @bsipocz in #258 (comment)