Update build-images.md (#12843)

* Update build-images.md

Small typos in the documentation, which may lead to confusion.

* Inspiration from node.js docs

Added documentation for why we copy `package*.json` before copying the whole directory. Checkout: https://nodejs.org/en/docs/guides/nodejs-docker-webapp/#creating-a-dockerfile. 
The node.js docs has more optimized code too (using `npm ci` instead of `npm install`) which can be used here too.

* Fixed review provided and removed some weird whitespaces

language/nodejs/build-images.md

@@ -145,7 +145,8 @@ Before we can run `npm install`, we need to get our `package.json` and `package-
 COPY ["package.json", "package-lock.json*", "./"]
 ```
 
-Once we have our `package.json` files inside the image, we can use the `RUN` command to execute the command npm install. This works exactly the same as if we were running npm install locally on our machine, but this time these Node modules will be installed into the `node_modules` directory inside our image.
+Note that, rather than copying the entire working directory, we are only copying the package.json file. This allows us to take advantage of cached Docker layers.
+Once we have our files inside the image, we can use the `RUN` command to execute the command npm install. This works exactly the same as if we were running npm install locally on our machine, but this time these Node modules will be installed into the `node_modules` directory inside our image.
 
 ```dockerfile
 RUN npm install --production