Update README with basic architecture section

Adding the description of the architecture extracted from the blog entry.

README.md

@@ -5,6 +5,14 @@ This is an example Docker app with multiple services. It is run with Docker Comp
 
 More info at https://blog.docker.com/2015/11/docker-toolbox-compose/
 
+Architecture
+-----
+
+* A Python webapp which lets you vote between two options
+* A Redis queue which collects new votes
+* A Java worker which consumes votes and stores them in…
+* A Postgres database backed by a Docker volume
+* A Node.js webapp which shows the results of the voting in real time
 
 Running
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