docs: fix aws ec2 readme inconsistency (#9567)

plugins/processors/aws/ec2/README.md

@@ -9,7 +9,7 @@ to metrics associated with EC2 instances.
 
 ```toml
 [[processors.aws_ec2]]
-  ## Tags to attach to metrics. Available tags:
+  ## Available tags:
   ## * accountId
   ## * architecture
   ## * availabilityZone
@@ -23,9 +23,19 @@ to metrics associated with EC2 instances.
   ## * ramdiskId
   ## * region
   ## * version
-  tags = []
+  imds_tags = []
 
-  ## Timeout for http requests made by against AWS EC2 metadata endpoint.
+  ## EC2 instance tags retrieved with DescribeTags action.
+  ## In case tag is empty upon retrieval it's omitted when tagging metrics.
+  ## Note that in order for this to work, role attached to EC2 instance or AWS
+  ## credentials available from the environment must have a policy attached, that
+  ## allows ec2:DescribeTags.
+  ##
+  ## For more information see:
+  ## https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeTags.html
+  ec2_tags = []
+
+  ## Timeout for http requests made by against aws ec2 metadata endpoint.
   timeout = "10s"
 
   ## ordered controls whether or not the metrics need to stay in the same order
@@ -35,6 +45,11 @@ to metrics associated with EC2 instances.
   ## depending on the order of metrics staying the same. If so, set this to true.
   ## Keeping the metrics ordered may be slightly slower.
   ordered = false
+
+  ## max_parallel_calls is the maximum number of AWS API calls to be in flight
+  ## at the same time.
+  ## It's probably best to keep this number fairly low.
+  max_parallel_calls = 10
 ```
 
 ## Example