Prod logging example (Example 2) omits loggers: ~, causes error 500

- Page: Administrator's manual → Maintenance → Logging → "Example 2: Enable high-level logging on production"

- Version: 2.10 (likely affects other versions too — same text appears at least back to 2.5)

- Issue: The default prod: config shown just above Example 2 correctly includes loggers: ~ when not using sfAggregateLogger — this matches Symfony's own documented requirement ("If you don't use the sfAggregateLogger, don't forget to specify a null value for the loggers parameter"). But the modified prod: block in Example 2 omits that line. Following the example as written causes AtoM to throw a fatal 500 error: Call to undefined method sfFileLogger::addLogger().

- Proposed fix: Add loggers: ~ to the Example 2 prod: logger param block, so it reads:

```diff
prod:
logger:
class: sfFileLogger
param:
level: warning
file: %SF_LOG_DIR%/qubit_prod.log
+ loggers: ~
```

Open Administrator's manual → Maintenance → Logging → “Example 2: Enable high-level logging on production” and compare its prod logger block with the default configuration immediately above. Add the missing loggers: ~ line shown in the proposed diff, then verify the example no longer produces the reported sfFileLogger error.

Written by the indexing model from the issue text.