Fix logging instrumentation example and output

Author: andremm

instrumentation/opentelemetry-instrumentation-logging/src/opentelemetry/instrumentation/logging/__init__.py

@@ -16,12 +16,13 @@
 
 """
 The OpenTelemetry `logging` integration automatically injects tracing context into
-log statements.
+log statements, though it is opt-in and must be enabled explicitly by setting the
+environment variable `OTEL_PYTHON_LOG_CORRELATION` to `true`.
 
-Usage
------
 .. code-block:: python
 
+    # export OTEL_PYTHON_LOG_CORRELATION=true
+
     import logging
 
     from opentelemetry.instrumentation.logging import LoggingInstrumentor
@@ -32,8 +33,27 @@
 
 When running the above example you will see the following output:
 ```
-WARNING:root:OTel test
+2025-03-05 09:40:04,398 WARNING [root] [example.py:7] [trace_id=0 span_id=0 resource.service.name= trace_sampled=False] - OTel test
 ```
+
+The environment variable `OTEL_PYTHON_LOG_CORRELATION` must be set to `true`
+in order to enable trace context injection into logs by calling
+`logging.basicConfig()` and setting a logging format that makes use of the
+injected tracing variables.
+
+Alternatively, `set_logging_format` argument can be set to `True` when
+initializing the `LoggingInstrumentor` class to achieve the same effect:
+
+.. code-block:: python
+
+    import logging
+
+    from opentelemetry.instrumentation.logging import LoggingInstrumentor
+
+    LoggingInstrumentor().instrument(set_logging_format=True)
+
+    logging.warning('OTel test')
+
 """
 
 import logging  # pylint: disable=import-self