docs(tracer): install section

Author: heitorlessa

docs/core/tracer.md

@@ -19,6 +19,12 @@ Tracer is an opinionated thin wrapper for [AWS X-Ray Python SDK](https://github.
 ???+ tip
     All examples shared in this documentation are available within the [project repository](https://github.com/awslabs/aws-lambda-powertools-python/tree/develop/examples){target="_blank"}.
 
+### Install
+
+!!! info "This is not necessary if you're using Lambda Layer"
+
+Add `aws-lambda-powertools[aws-xray-sdk]` in your preferred dependency management tool.
+
 ### Permissions
 
 Before your use this utility, your AWS Lambda function [must have permissions](https://docs.aws.amazon.com/lambda/latest/dg/services-xray.html#services-xray-permissions) to send traces to AWS X-Ray.