[cloud][docs] Add more EC2 dynamic inventory stack_filter docs

contrib/inventory/ec2.ini

@@ -153,8 +153,10 @@ group_by_elasticache_replication_group = True
 # Filters are key/value pairs separated by '=', to list multiple filters use
 # a list separated by commas. See examples below.
 
-# If you want to apply multiple filters simultaneously, uncomment and set to True. 
-# Default behaviour is to apply filters one by one and concatenate results.
+# If you want to apply multiple filters simultaneously, set stack_filters to
+# True. Default behaviour is to combine the results of all filters. Stacking
+# allows the use of multiple conditions to filter down, for example by
+# environment and type of host.
 stack_filters = False
 
 # Retrieve only instances with (key=value) env=staging tag