Add Vonage wordmark to Nexmo repo

Author: lornajane

README.md

@@ -1,5 +1,7 @@
 # Nexmo Code Snippets for Python
 
+<img src="https://developer.nexmo.com/assets/images/Vonage_Nexmo.svg" height="48px" alt="Nexmo is now known as Vonage" />
+
 Code snipets also available for: [Java](https://github.com/nexmo/nexmo-java-code-snippets), [.NET](https://github.com/nexmo/nexmo-dotnet-code-snippets), [Node.js](https://github.com/nexmo/nexmo-node-code-snippets), [PHP](https://github.com/nexmo/nexmo-php-code-snippets), [Ruby](https://github.com/nexmo/nexmo-ruby-code-snippets), [Curl](https://github.com/Nexmo/nexmo-curl-code-snippets) and [Android](https://github.com/nexmo-community/quickstart-android)
 
 The purpose of the Code Snippets is to provide simple examples focused