docs(ecs): Fix ecs readme markdown (#16018)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-ecs/README.md

@@ -909,7 +909,7 @@ taskDefinition.addContainer('cont', {
 
 Please note, ECS Exec leverages AWS Systems Manager (SSM). So as a prerequisite for the exec command
 to work, you need to have the SSM plugin for the AWS CLI installed locally. For more information, see
-[Install Session Manager plugin for AWS CLI] (https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html).
+[Install Session Manager plugin for AWS CLI](https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html).
 
 To enable the ECS Exec feature for your containers, set the boolean flag `enableExecuteCommand` to `true` in
 your `Ec2Service` or `FargateService`.