Add French docstrings and README

- Docstrings for all modules, classes and methods
- README.md with installation and usage instructions
- Update CLAUDE.md with dns.py

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -24,7 +24,7 @@ python lan_checker.py
 - `lan_checker.py` - Main script: config loading, MQTT client, check scheduler
 - `checkers/` - Modular check implementations
   - `base.py` - `BaseChecker` abstract class and `CheckResult` dataclass
-  - `ping.py`, `http.py`, `snmp.py` - Concrete checker implementations
+  - `ping.py`, `http.py`, `dns.py`, `snmp.py` - Concrete checker implementations
 - `config.yaml.example` - Configuration template (copy to `config.yaml`)
 
 ## Adding a New Checker