Add --exit-non-zero-on-format to formatter exit codes section (#22761)

Author: alejsdev

docs/formatter.md

@@ -364,6 +364,7 @@ When an incompatible lint rule or setting is enabled, `ruff format` will emit a
 `ruff format` exits with the following status codes:
 
 - `0` if Ruff terminates successfully, regardless of whether any files were formatted.
+- `1` if Ruff terminates successfully, one or more files were formatted, and `--exit-non-zero-on-format` was specified.
 - `2` if Ruff terminates abnormally due to invalid configuration, invalid CLI options, or an
     internal error.