docs: split InfoMetricFamily example into two separate blocks

The single block with two yield statements looked like one collect() yielding
both patterns. Split into labelled prose + code pairs to make clear they are
alternatives, not sequential yields.

Signed-off-by: k1chik <kkukdia@gmail.com>

Author: k1chik

docs/content/collector/custom.md

@@ -241,11 +241,15 @@ InfoMetricFamily(name, documentation, value=None, labels=None)
 | `value` | `Dict[str, str]` | Key-value label pairs that form the info payload. |
 | `timestamp` | `float` or `Timestamp` | Optional Unix timestamp. |
 
+Single unlabelled info metric:
+
 ```python
-# single unlabelled info metric
 yield InfoMetricFamily('build', 'Build metadata', value={'version': '1.2.3', 'commit': 'abc123'})
+```
 
-# labelled: one info metric per service
+Labelled — one info metric per service:
+
+```python
 i = InfoMetricFamily('service_build', 'Per-service build info', labels=['service'])
 i.add_metric(['auth'], {'version': '2.0.1', 'commit': 'def456'})
 i.add_metric(['api'], {'version': '1.9.0', 'commit': 'ghi789'})