community: add link to digitalocean tutorial

Signed-off-by: Marko Mudrinić <mudrinic.mare@gmail.com>

community.md

@@ -108,6 +108,7 @@ Key:
 
 | Blog/repo name and description                                          | Author       | Site     | Date        |
 |---------------------------------------------------------------------|--------------|----------|-------------|
+| [How To Install and Secure OpenFaaS Using Docker Swarm on Ubuntu 16.04](https://www.digitalocean.com/community/tutorials/how-to-install-and-secure-openfaas-using-docker-swarm-on-ubuntu-16-04) | Marko Mudrinić | digitalocean.com | 19-Sept-2018 |
 | [Vert.x + Graal = Java for Serverless = ❤️!](https://www.jetdrone.xyz/2018/09/07/Vertx-Serverless-5mb.html) | Paulo Lopes | jetdrone.xyz | 07-Sept-2018 |
 | [OpenFass 介绍及源码分析 (OpenFaaS Deep-Dive / Code-Analysis) - Chinese](https://www.youtube.com/watch?v=bZtgrAVR9HQ&feature=youtu.be) | Zhu Zhenfeng | youtube.com | 07-Sept-2018 |
 | [Introducing stateless microservices for OpenFaaS](https://www.openfaas.com/blog/stateless-microservices/) | Alex Ellis | openfaas.com | 05-Sept-2018 |