add sample app readme

Author: srprash

sample-apps/apigateway-lambda/README.md

@@ -0,0 +1,58 @@
+## API Gateway + Lambda Sample Application
+
+The directory contains the source code and the Infrastructure as Code (IaC) to create the sample app in your AWS account.
+
+### Prerequisite
+Before you begin, ensure you have the following installed:
+- Java 17
+- Gradle
+- Terraform
+- AWS CLI configured with appropriate credentials
+
+### Getting Started
+
+#### 1. Build the application
+```bash
+# Change to the project directory
+cd sample-apps/apigateway-lambda
+
+# Build the application using Gradle
+gradle clean build
+
+# Prepare the Lambda deployment package
+gradle createLambdaZip
+```
+
+#### 2. Deploy the application
+```bash
+# Change to the terraform directory
+cd terraform
+
+# Initialize Terraform
+terraform init
+
+# (Optional) Review the deployment plan for better understanding of the components
+terraform plan
+
+# Deploy
+terraform apply
+```
+
+#### 3. Testing the applicating
+After successful deployment, Terraform will output the API Gateway endpoint URL. You can test the application using:
+```bash
+curl <API_Gateway_URL>
+```
+
+#### 4. Clean Up
+To avoid incurring unnecessary charges, remember to destroy the resources when you are done:
+```bash
+terraform destroy
+```
+
+#### (Optional) Instrumenting with Application Signals Lambda Layer
+You can choose to instrument the Lambda function with Application Signals Lambda Layer upon deployment by passing in the layer ARN to the `adot_layer_arn` variable.
+You must have the layer already published to your account before executing the following command.
+```bash
+terraform apply -var "adot_layer_arn=<APPLICATION_SIGNALS_LAYER_FULL_ARN_WITH_VERSION>"
+```