Improve privacy, security, and encryption documentation #896

[micahellison]

Fixes #896. Adds a new section on privacy/security and addresses the points in the related issue.

Checklist

• The code change is tested and works locally. Reviewed locally w/ poetry run mkdocs serve
• Tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?

[wren]

🧳