Add --init to run example

Wrap process with the light-weight Docker init system, to handle SIGTERM
and reap process as expected. This is a recommended best practice for
running Node apps in Docker.

Author: lingmann

Dockerfile

@@ -1,6 +1,6 @@
 # To use this with Docker:
 # 1. `docker build -t iftttdelay .`
-# 2. `docker run -p 3002:3002 -d iftttdelay`
+# 2. `docker run -p 3002:3002 -d --init iftttdelay`
 # The service will now be listening on http://localhost:3002
 
 FROM node:10.11-alpine