Update arg to node_version (#129)

* Update node version argument and comments

Dockerfile

@@ -1,15 +1,16 @@
 # Pass in nodejs version
-ARG NODE_MAJOR=20.0.0
+ARG NODE_VERSION=20.0.0
 
 # Pull in the nodejs image
-FROM node:${NODE_MAJOR}-alpine AS node
+FROM node:${NODE_VERSION}-alpine AS node
 
 # Pull in relevant ruby image
 FROM ruby:3.2.2-alpine
 
-# As it is a multistage build
-# We will pull in the contents from the previous node image
-# To our current ruby image
+# As this is a multistage Docker image build
+# we will pull in the contents from the previous node image build stage
+# to our current ruby build image stage
+# so that the ruby image build stage has the correct nodejs version
 COPY --from=node /usr/lib /usr/lib
 COPY --from=node /usr/local/share /usr/local/share
 COPY --from=node /usr/local/lib /usr/local/lib