Insured we're on a recent & Long Time Support (LTS) version of node.

Also added some helpful comment to explain what is doing what and the choices made.

Dockerfile

@@ -1,8 +1,15 @@
-FROM node:0.10-onbuild
+# The base image is the latest 4.x node (LTS) on jessie (debian)
+# -onbuild will install the node dependencies found in the project package.json
+# and copy its content in /usr/src/app, its WORKDIR
+FROM node:4-onbuild
 
 ENV NODE_ENV=production \
     daemon=false \
     silent=false
 
+# nodebb setup will ask you for connection information to a redis (default), mongodb then run the forum
+# nodebb upgrade is not included and might be desired
 CMD node app --setup && npm start
+
+# the default port for NodeBB is exposed outside the container
 EXPOSE 4567