added docker image info to readme

Author: jakewmeyer

README.md

@@ -87,3 +87,7 @@ See the [Contribution](https://github.com/r-spacex/SpaceX-API/blob/master/CONTRI
 * Uses [Travis CI](https://travis-ci.org/) for testing + deployment
 * All data stored as [MongoDB](https://www.mongodb.com/) documents
 * API is deployed on a [Heroku](https://www.heroku.com/) pipeline with staging and production servers
+* A [Docker](https://hub.docker.com/r/jakewmeyer/spacex-api/) image is avaiable for local development
+```Docker
+docker pull jakewmeyer/spacex-api
+```