Adds explanation about all_elasticache_nodes and all_elastic_clusters settings

plugins/inventory/ec2.ini

@@ -65,6 +65,11 @@ all_rds_instances = False
 # By default, only ElastiCache clusters and nodes in the 'available' state
 # are returned. Set 'all_elasticache_clusters' and/or 'all_elastic_nodes'
 # to True return all ElastiCache clusters and nodes, regardless of state.
+#
+# Note that all_elasticache_nodes only applies to listed clusters. That means
+# if you set all_elastic_clusters to false, no node will be return from
+# unavailable clusters, regardless of the state and to what you set for
+# all_elasticache_nodes.
 all_elasticache_replication_groups = False
 all_elasticache_clusters = False
 all_elasticache_nodes = False