Add comprehensive documentation for sync commands and Docker usage

[wirwolf]

Summary

This PR adds extensive documentation for the sync command suite and Docker deployment options to the README. The changes provide users with detailed guidance on using the vault-manager tool for syncing secrets between Vault and local JSON files.

Key Changes

• sync pull command: Documented the download functionality with conflict resolution behavior (automatic for new secrets, interactive for conflicts, non-TTY defaults to remote)
• sync plan command: Documented the read-only diff operation with change indicators (+, ~, -) and summary output format
• sync apply command: Documented the write operation with confirmation prompt, add/modify/delete behaviors, and JSON serialization details
• Local JSON file format: Documented the storage format including pretty-printing, automatic JSON expansion for nested objects, and re-serialization on apply
• Docker usage: Added comprehensive Docker examples covering:
  • One-off commands
  • Reading secrets
  • sync pull/plan/apply operations with proper volume mounts
  • Environment variable configuration as alternative to config files
  • TLS verification options
  • docker-compose example with full service definition

Notable Details

• Clearly explains the interactive conflict resolution in pull with specific behavior for TTY vs non-TTY environments
• Provides a reference table for change indicators in the plan command
• Includes practical Docker examples with proper flag usage (-it for interactive, -i for piped input)
• Documents automatic JSON expansion/serialization for nested objects to maintain human-readability

https://claude.ai/code/session_01Xb7eRse5ys7GHz8q4CvTj9