Update README to list required IAM permission: logs:DescribeLogGroups. (#75)

The permission logs:DescribeLogGroups is used by aws_common to list CloudWatch log groups to determine if the log group used by cloudwatch_logger exists.

Signed-off-by: Zachary Michaels <[email protected]>

Author: zmichaels11

README.md

@@ -42,6 +42,7 @@ You will need to create an AWS Account and configure the credentials to be able
 
 This node will require the following AWS account IAM role permissions:
 - `logs:PutLogEvents`
+- `logs:DescribeLogGroups`
 - `logs:DescribeLogStreams`
 - `logs:CreateLogStream`
 - `logs:CreateLogGroup`