docs: add newsletter badge

README.md

@@ -14,7 +14,8 @@
 [![Security Rating](https://sonarcloud.io/api/project_badges/measure?project=wiki&metric=security_rating)](https://sonarcloud.io/dashboard?id=wiki)
 [![Standard - JavaScript Style Guide](https://img.shields.io/badge/code%20style-standard-brightgreen.svg?style=flat)](http://standardjs.com/)  
 [![Chat on Gitter](https://img.shields.io/badge/chat-on_gitter-CC2B5E.svg?style=flat&logo=image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAcAAAAOCAMAAADUg/YpAAAABlBMVEUAAAD///%2Bl2Z/dAAAAAXRSTlMAQObYZgAAABVJREFUeAFjwAUYYTQByAAh0WicAAAFnwAYeB5bLwAAAABJRU5ErkJggg==)](https://gitter.im/Requarks/wiki)
-[![Twitter Follow](https://img.shields.io/badge/follow-%40requarks-blue.svg?style=flat)](https://twitter.com/requarks)
+[![Twitter Follow](https://img.shields.io/badge/follow-%40requarks-blue.svg?style=flat&logo=twitter)](https://twitter.com/requarks)
+[![Subscribe to Newsletter](https://img.shields.io/badge/newsletter-subscribe-yellow.svg?style=flat&logo=mailchimp)](https://wiki.requarks.io/newsletter)
 
 ##### A modern, lightweight and powerful wiki app built on NodeJS