PROJECT: Revise Airgap, practices of separation/partitioning, #writing

Curent Draft: https://hackmd.io/aZkGa42WRbeayRBdNykTSg

(incomplete, and needs revision)
- update with Ledger stuff?

Article to respond to criticisms of airgap technology addressed in recent multisig-scenario PR [#15](https://github.com/BlockchainCommons/SmartCustody/issues/15), gordian & smart custody practices of functional seperatation/partitioning (such as https://github.com/BlockchainCommons/SmartCustody/blob/master/Docs/Practices.md#separate-seeds--keys), etc.) and separate ecosystem roles.

Other related articles:
* https://shiftcrypto.ch/blog/does-airgap-make-bitcoin-hardware-wallets-more-secure/
* https://www.computer.org/publications/tech-news/trends/qr-code-risks
* https://www.techradar.com/features/do-not-overlook-the-security-risk-posed-by-qr-codes

Related minor task. Decide on our language here (separation? partitioning? segregation) and make consistent in SmartCustody and Gordian repos.

- [ ] Consider beyond Service Separation to Hardware Separation (for if Keys are in different place)
- [ ] API Separation
- [ ] Is this a musings article?

(Separate articles? General pattern? Look for where you can separate things to improve reliability, reduce collusion, reduce single-service attacks)