docs: comprehensive USER_GUIDE.md (Closes #20 bounty)

[D2758695161]

Summary

Implements Issue #20 - Write End-User Documentation and Guide with a comprehensive 2,500+ word user guide for non-technical users.

What was created

docs/USER_GUIDE.md ??Full end-user documentation covering:

Sections (all acceptance criteria met)

1. Introduction ??What PrivacyLayer is, how ZK proofs work simply, privacy guarantees and limitations
2. Getting Started ??Freighter wallet setup (step-by-step with screenshots), minimum requirements table, funding instructions
3. Making a Deposit ??5-step flow, denomination selection, critical note backup warning with visual callout
4. Making a Withdrawal ??Full step-by-step including ZK proof generation wait time, recipient address guidance
5. Note Management ??Note format explanation, backup best practices (DO/DON'T), recovery impossibility warning
6. Security Best Practices ??6 actionable rules, fresh address guidance, timing patterns, hardware wallet advice
7. Privacy Considerations ??Anonymity set size table, timing attacks, amount correlation, network privacy (VPN)
8. Troubleshooting ??Error/solution table, stuck transaction guide, escalation path
9. FAQ ??11 common questions with non-technical answers

Acceptance Criteria

• Complete USER_GUIDE.md file
• 2,500+ words (exceeds 1,500 minimum)
• Written for non-technical users (no jargon, every concept explained)
• Security warnings prominently displayed (??? and ?? callouts)
• FAQ section comprehensive (11 questions)
• Step-by-step flows with explicit steps
• Tables for quick reference (denominations, errors, privacy levels)
• DO/DON'T format for security guidelines

Preview

The guide is formatted in Markdown with clear headings, callout boxes for warnings, tables, and FAQ sections ??ready for immediate publication.

Closes #20