docs(envelopes): create comprehensive documentation

[j-d-ha]

Description

Create comprehensive documentation for all envelope types.

Tasks

• Update main README with envelope overview
• Create envelope selection guide
• Add quick-start examples for each envelope type
• Add troubleshooting and FAQ section
• Link all envelope documentation

Acceptance Criteria

• Clear guidance on which envelope to use
• Complete examples for all envelope types
• Troubleshooting common issues
• FAQ section addressing common questions