Add documentation for debug logs environment variables. (#2186)

docs/userguide/connections.rst

@@ -64,6 +64,20 @@ resources:
     with Connection() as connection:
         # work with connection
 
+.. _debug-logs:
+
+Debug Logs
+==========
+
+Kombu exposes multiple environment variables that control debug logging for connection and channel logs.
+This is useful for situations where you want to debug Kombu or contribute to the project.
+
+If ``KOMBU_LOG_CONNECTION`` is set to 1, debug logs are enabled for connections.
+
+If ``KOMBU_LOG_CHANNEL`` is set to 1, debug logs are enabled for channels.
+
+If ``KOMBU_LOG_DEBUG`` is set to 1, debug logs are enabled for both connections and channels.
+
 .. _connection-urls:
 
 Celery with SQS