Added README for voice APIs (#21)

* README for voice APIs was missing, so added one :) * Updated with link to tutorials

Author: sanketsingh24

voice/README.md

@@ -0,0 +1,14 @@
+# Getting Started with Nexmo Voice APIs with PHP
+
+## Set up the ENV with Your Nexmo API Keys
+
+To use this sample you will first need a [Nexmo account](https://dashboard.nexmo.com/sign-up). Once you have your own API credentials, rename
+the `.env-example` file to `.env` and set the values as required.
+
+You also need to [buy a number](https://dashboard.nexmo.com/buy-numbers) where you can send and receive SMS messages.
+
+## Run the Examples
+
+To run Voice APIs, you need to set up your secure Nexmo Application first. You can use [Nexmo CLI tool](https://github.com/Nexmo/nexmo-cli) to create and manage your Nexmo Applications.
+
+For more information, read the [tutorials](https://developer.nexmo.com/voice/voice-api/tutorials).