docs(validation): add install section

Signed-off-by: heitorlessa <[email protected]>

Author: heitorlessa

docs/utilities/validation.md

@@ -18,6 +18,14 @@ This utility provides JSON Schema validation for events and responses, including
 ???+ 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 installing Powertools via [Lambda Layer](../index.md#lambda-layer){target="_blank"}"
+
+Add `aws-lambda-powertools[validation]` as a dependency in your preferred tool: _e.g._, _requirements.txt_, _pyproject.toml_.
+
+This will ensure you have the required dependencies before using Validation.
+
 You can validate inbound and outbound events using [`validator` decorator](#validator-decorator).
 
 You can also use the standalone `validate` function, if you want more control over the validation process such as handling a validation error.