Add details on docker

README.md

@@ -3,6 +3,13 @@
 
 ## Start docker 
 
+Docker will run mongodb in a container. You can optionally use node with express to expose a HTTP API.
+
+You have two options for the HTTP API:
+
+- run locally with node (option 1)
+- run node in a container (option 2)
+
 ### Option 1 (mongo containerized, node locally)
 
 build and run MongoDB and Node.js API with `orders.json` dump: