build(docker): Add comments to the docker config files to make them e…

…asy to understand.

Dockerfile

@@ -1,9 +1,30 @@
+# The Dockerfile is the description of all the commands to run to assemble the image.
+# Read about all the commands here: https://docs.docker.com/engine/reference/builder/
+
+# We also have a docker-compose.yml file, which is used to build and run this Docker image.
+
+
+# Start from the official Node 6 alpine image. https://hub.docker.com/_/node/
 FROM node:6-alpine
 
-COPY . /app
+# Set the working directory for following commands.
 WORKDIR /app
 
+# Copy only the files necessary to install dependencies into the working directory.
+# Docker builds the image in layers and caches them. Because the app files change more often than the dependencies, we
+#  copy the app files only after we install the depencendies.
+COPY package.json yarn.lock .npmrc ./
+
+# Install dependencies.
 RUN yarn install
+
+# Copy all source and test files into the working directory.
+# We use a .dockerignore file to prevent unnecessary or large files from being inadvertently copied.
+COPY . /app
+
+# Build the app.
 RUN yarn build
 
+# The entrypoint configures the container to be run as an executable.
+# Arguments supplied on the command line will be forwarded onto the entrypoint.
 ENTRYPOINT ["yarn"]

docker-compose.yml

@@ -1,3 +1,14 @@
+# The docker-compose.yml describes all the services in our application. While Docker Compose is best suited for
+#  multi-container applications, we can use it to simplify our interaction with Docker.
+#  https://docs.docker.com/compose/overview/
+
+# `docker-compose build` --> Build the image. Do this first.
+# `docker images` --> View the image you just built
+
+# `docker-compose run lib <command>` --> <command> and any arguments will be forwarded onto the Dockerfile entrypoint, "yarn".
+# `docker-compose run lib test` --> Run tests.
+# `docker-compose run --service-ports lib start:styleguide` --> Start the styleguidist dev server.
+
 version: '3'
 services:
   lib: