- Clarify SFTP uses SSH key authentication instead of password
- Generalize destination server user description to be more flexible
- Improve SSH key setup instructions with clearer step-by-step guidance
- Update test command output message for better clarity
- Simplify section headers and remove redundant logs section
Add comprehensive documentation covering SSH key generation, environment
variable configuration, cron scheduling, and log file management for the
automated backup system on Debian 12.