docs: add amplify-cli instructions for public layer (aws-powertools#754)

Author: AlessandroVol23

docs/index.md

@@ -131,6 +131,32 @@ We build, release and distribute packaged Lambda Powertools layers for each regi
 
  ```
 
+=== "Amplify"
+
+ ```zsh
+ # Create a new one with the layer
+ ❯ amplify add function
+ ? Select which capability you want to add: Lambda function (serverless function)
+ ? Provide an AWS Lambda function name: <NAME-OF-FUNCTION>
+ ? Choose the runtime that you want to use: Python
+ ? Do you want to configure advanced settings? Yes
+ ...
+ ? Do you want to enable Lambda layers for this function? Yes
+ ? Enter up to 5 existing Lambda layer ARNs (comma-separated): arn:aws:lambda:eu-central-1:017000801446:layer:AWSLambdaPowertoolsPython:3
+ ❯ amplify push -y
+
+ 
+ # Updating an existing function and add the layer
+ ❯ amplify update function
+ ? Select the Lambda function you want to update test2
+ General information
+ - Name: <NAME-OF-FUNCTION>
+ ? Which setting do you want to update? Lambda layers configuration
+ ? Do you want to enable Lambda layers for this function? Yes
+ ? Enter up to 5 existing Lambda layer ARNs (comma-separated): arn:aws:lambda:eu-central-1:017000801446:layer:AWSLambdaPowertoolsPython:3
+ ? Do you want to edit the local lambda function now? No
+ ```
+
 ??? note "Layer ARN per region"
 
  !!! tip "Click to copy to clipboard"