Add info to the monolog.channels config

Author: GromNaN

src/DependencyInjection/Configuration.php

@@ -416,6 +416,7 @@ public function getConfigTreeBuilder(): TreeBuilder
             ->children()
                 ->scalarNode('use_microseconds')->defaultTrue()->end()
                 ->arrayNode('channels')
+                    ->info('List of additional channels to create. The "app" channel is already created by default.')
                     ->canBeUnset()
                     ->prototype('scalar')->end()
                 ->end()