Move information from readme into xmidt.io site

[joe94]

@kristinaspring pointed out that portions of the readme #Details component (those after endpoints) are a better fit to be listed under the "Operating" section in https://xmidt.io/docs/operating/getting_started/

Task: Add a Themis section for themis.

[kristinapathak]

I think this might be better to be put into the docs repo:
https://github.com/xmidt-org/docs