Adds a note about RedisTimeSeries.

Author: Simon Prickett

README.md

@@ -13,6 +13,7 @@ In order to start and run this application, you will need:
 * [Node.js](https://nodejs.org/en/download/) (8.9.4 or newer, we recommend using the current Long Term Stable version)
 * npm (installed with Node.js)
 * Access to a local or remote installation of [Redis](https://redis.io/download) version 5 or newer (local preferred)
+* If you want to try the RedisTimeSeries exercises, you'll need to make sure that your Redis installation also has the [RedisTimeSeries Module](https://oss.redislabs.com/redistimeseries/) installed
 
 # Setup