Update comments

docker/Dockerfile

@@ -1,3 +1,5 @@
+# A multistage Dockerfile. The first stage is the builder image then
+# we copy all needed dependencies to the final image to reduce size
 FROM node:lts-alpine as builder
 
 # Install dependencies
@@ -24,6 +26,7 @@ FROM node:lts-alpine as server
 
 WORKDIR /app
 
+# Copy the application from the previous stage (without extra packages installed through apk/apt)
 COPY --from=builder /app ./
 
 # Expose the port and start the application