Updated usage details in README

Author: jamesmcroft

README.md

@@ -14,6 +14,61 @@ The Opayo (formerly SagePay) Form Integration Library for JavaScript is a librar
 npm install opayo-form-integration-for-js
 ```
 
+## Usage
+
+### Initiating a payment
+
+```js
+import { TransactionService, ITransaction, ITransactionDetail } from 'opayo-form-integration-for-js';
+
+var transactionService = new TransactionService();
+
+var transactionDetail = {
+    "VendorTxCode": "PaymentReference-1",
+    "Amount": "10.00",
+    "Currency": "GBP",
+    "Description": "Test transaction",
+    "SuccessURL": "https://www.example.com/success",
+    "FailureURL": "https://www.example.com/failure",
+    "CustomerName": "John Smith",
+    "CustomerEMail": "john.smith@email.com",
+    "BillingSurname": "Smith",
+    "BillingFirstnames": "John",
+    "BillingAddress1": "1 High Street",
+    "BillingCity": "London",
+    "BillingPostCode": "EC1N 2TD",
+    "BillingCountry": "GB",
+    "DeliverySurname": "Smith",
+    "DeliveryFirstnames": "John",
+    "DeliveryAddress1": "1 High Street",
+    "DeliveryCity": "London",
+    "DeliveryPostCode": "EC1N 2TD",
+    "DeliveryCountry": "GB",
+    } as ITransactionDetail;
+
+/*
+ * Initiate transaction will return the object that has been transmitted to Opayo's Form Integration page in case you need it for reference.
+ * Calling this method will automatically submit the data to Opayo and redirect the user to Opayo's Form Integration page.
+ */
+var transaction = await transactionService.initiateTransaction(transactionDetail, "opayotest", "your_encryption_password") as ITransaction;
+```
+
+### Handling a response
+
+```js
+import { TransactionService, ITransactionResponse } from 'opayo-form-integration-for-js';
+
+var transactionService = new TransactionService();
+
+/*
+ * You will first need to grab the crypt value from the query string of the return URL from Opayo's Form Integration page.
+ * Passing that value into the `handleTransactionResponse` method will decrypt the response using your Opayo Form Integration encryption password and return it.
+ */
+var urlParams = new URLSearchParams(window.location.search);
+var crypt = urlParams.get('crypt');
+var response = await transactionService.handleTransactionResponse(crypt, "your_encryption_password") as ITransactionResponse;
+```
+
 ## Contributing 🤝🏻
 
 Contributions, issues and feature requests are welcome!

src/TransactionService.ts

@@ -59,7 +59,7 @@ export class TransactionService implements ITransactionService {
         "PurchaseInstalData": new ValidatorArray(() => { }, new RegexValidator(/^\d+$/), new MaxLengthValidator(3)),
     }
 
-    constructor(isTestEnvironment: boolean) {
+    constructor(isTestEnvironment: boolean = false) {
         this.isTestEnvironment = isTestEnvironment;
     }