(cloudwatch) add document for new query

docs/sources/datasources/cloudwatch.md

@@ -64,9 +64,19 @@ Name | Description
 `metrics(namespace)` | Returns a list of metrics in the namespace.
 `dimension_keys(namespace)` | Returns a list of dimension keys in the namespace.
 `dimension_values(region, namespace, metric, dimension_key)` | Returns a list of dimension values matching the specified `region`, `namespace`, `metric` and `dimension_key`.
+`ebs_volume_ids(region, instance_id)` | Returns a list of volume id matching the specified `region`, `instance_id`.
+`ec2_instance_attribute(region, attribute_name, filters)` | Returns a list of attribute matching the specified `region`, `attribute_name`, `filters`.
 
 For details about the metrics CloudWatch provides, please refer to the [CloudWatch documentation](https://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/CW_Support_For_AWS.html).
 
+The `ec2_instance_attribute` query take `filters` in JSON format.  
+You can specify [pre-defined filters of ec2:DescribeInstances](http://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html).  
+Specify like `{ filter_name1: [ filter_value1 ], filter_name2: [ filter_value2 ] }`
+
+Example `ec2_instance_attribute()` query
+
+    ec2_instance_attribute(us-east-1, InstanceId, { "tag:Environment": [ "production" ] })
+
 ![](/img/v2/cloudwatch_templating.png)
 
 ## Cost