Deprecating the Psych-DS README as a centralized hub in favor of readthedocs

[bleonar5]

For the most part, after updating the readthedocs this week and looking through this repo's README, I don't think there's anything strictly necessary here that doesn't also appear somewhere in the docs.

• There is no link to the "technical spec" on the readthedocs, but I think we've deprecated that document and checked that everything essential within it is included. In addition to adding a prominent link to the readthedocs within this README, I think we could afford at this point to remove the technical spec.
• The readthedocs now does reference (and provide a link to) the "code of conduct" for community contributions, but perhaps we could give the actual text of this code of conduct its own page on the readthedocs? It could either live there redundantly, or we could remove it from this repo.
• The license from this repository is not reflected in the readthedocs, but maybe in terms of conventional practices that makes sense? these licenses do usually live in repositories rather than readthedocs-es.
• The readthedocs does not currently have a "team" or "about us" page, which is information that the README currently includes. Should we include something like that?
• Another difference between this README and the readthedocs is that the README includes anecdotal history of how Psych-DS came to be ("SIPS", etc). Is something like this important to move over to the docs?
• The docs does not list any of the "links from earlier in psych-DS's life" from the bottom of the readme, but it does include the other resources linked above them.