Add new documentation explaining how Helmfile merges values from various sources:
- Core architecture and data flow
- Values sources and precedence order
- Deep merge behavior for maps and arrays
- Environment-specific value handling
- Secret management and priorities
- Common patterns and troubleshooting
This guide helps users understand the foundational concepts needed for
writing effective helmfiles, especially regarding value overrides and
merge strategies.
Signed-off-by: yxxhero <aiopsclub@163.com>