explain uid and log levels

plugins/logger.rst

@@ -26,6 +26,11 @@ compliant logger::
         [$loggerPlugin]
     );
 
+The log level for exceptions is `error`, the request and responses without exceptions are logged at level `info`.
+Request and response/errors can be correlated by looking at the `uid` of the log context.
+If you don't want to normally log requests, you can set the logger to normally only log `error` but use the
+Fingerscrossed logger of monolog to also log the request in case an exception is encountered.
+
 By default it uses ``Http\Message\Formatter\SimpleFormatter`` to format the request or the response into a string.
 You can use any formatter implementing the ``Http\Message\Formatter`` interface::