DO NOT MERGE - Document the TAD concept and Rockwell origins

[JFWooten4]

Reorients the README around the historical Transfer Agent Depository concept before the protocol-development notes.

• leads with the SEC's direct 2015 Transfer Agent Regulations report
• connects TAD3 explicitly to the 1969 North American Rockwell Securities Industry Overview study
• includes short SEC quotations describing the decentralized TAD model
• gives the specific Rockwell page references preserved in SEC footnotes 19, 52, and 53
• distinguishes the historical TAD architecture from TAD3's Web3 implementation

The historical report is Rockwell, not Rockefeller; the SEC release is the direct primary regulatory source and is available as an SEC-hosted PDF.

[JFWooten4]

This needs the Google scan ref from https://www.congress.gov/bill/94th-congress/senate-bill/249 in the original introduction post. Should move into the docs repo and address blocktransfer/website#17