Add Dockerfile commentary

Dockerfile

@@ -1,9 +1,6 @@
-FROM rust:1.77.2-alpine3.18 AS builder
-
-WORKDIR /app
-COPY . .
-
-RUN apk add --no-cache musl-dev
-RUN cargo install --path .
-
-CMD [ "/usr/local/cargo/bin/rust-rocket-counter-api" ]
+FROM rust:1.77.2-alpine3.18                                  # Base image
+WORKDIR /app                                                 # Working directory
+COPY . .                                                     # Copy application code and dependencies
+RUN apk add --no-cache musl-dev                              # Install OS dependencies
+RUN cargo install --path .                                   # Build the application
+CMD [ "/usr/local/cargo/bin/rust-rocket-counter-api" ]       # Run the application