add parameter to build docker container in development mode

Dockerfile

@@ -1,18 +1,20 @@
 # DESCRIPTION: publicbodies.org website
 # BUILD: docker build --rm -t publicbodies .
 # 
-# If you want to just build the documentation portal locally, do:
-#   docker build --rm -t publicbodies .
+# If you want to build the portal locally in development mode, do:
+#   docker build --rm -t publicbodies . --build-arg NODE_ENV=development
 # to build the container, then run
 #   docker run --rm --name publicbodies -p 3000:3000 -it publicbodies node index.js
 # open http://localhost:3000 on your browser to see the portal.
 
 FROM node:12
 
+ARG NODE_ENV=production
+
 # Never prompt the user for choices on installation/configuration of packages
 ENV DEBIAN_FRONTEND noninteractive
 ENV TERM linux
-ENV NODE_ENV=production
+ENV NODE_ENV=$NODE_ENV
 # from https://github.com/nodejs/docker-node/blob/main/docs/BestPractices.md#global-npm-dependencies
 ENV NPM_CONFIG_PREFIX=/home/node/.npm-global
 ENV PATH=$PATH:/home/node/.npm-global/bin

README.md

@@ -51,6 +51,13 @@ The website is a node webapp. To get it running:
         ```
         docker build --rm -t publicbodies .
         ```
+
+  If you are building a development environment, please use:
+
+        ```
+        docker build --rm -t publicbodies . --build-arg NODE_ENV=development
+        ```
+  so that you can get debugging information.
 
 4. Run the webapp: