added reference to blog article

README.md

@@ -1,6 +1,9 @@
 # flask-postgres-nginx-docker-compose
 MVP repo to have default config to run flask, postgres, and nginx running and networked with docker-compose
 
+## Prerequisites
+- Create `.env.dev` file in root of project based on `.env.dev-sample`
+
 ## Local
 - `docker-compose up`
 - Go to url: [http://localhost:8000/](http://localhost:8000/)
@@ -14,4 +17,7 @@ MVP repo to have default config to run flask, postgres, and nginx running and ne
 `docker rmi $(docker images -a -q)`
 
 ### Cleanup System
-`docker system prune`
+`docker system prune`
+
+### Reference
+- From: [blog](https://testdriven.io/blog/dockerizing-flask-with-postgres-gunicorn-and-nginx/)