Document alternative builder for scratch image

docker/scratch.Dockerfile

@@ -45,3 +45,32 @@ COPY --from=builder /app/target/x86_64-unknown-linux-musl/release/small-rust ./
 USER small-rust:small-rust
 
 CMD ["/app/small-rust"]
+
+####################################################################################################
+## Alternatively use this builder (image size actually bigger)
+####################################################################################################
+#FROM rust:1-alpine3.19 AS builder
+#
+#RUN rustup update nightly; rustup default nightly;
+#
+## Create appuser
+#ENV USER=small-rust
+#ENV UID=10001
+#
+#RUN adduser \
+#    --disabled-password \
+#    --gecos "" \
+#    --home "/nonexistent" \
+#    --shell "/sbin/nologin" \
+#    --no-create-home \
+#    --uid "${UID}" \
+#    "${USER}"
+#
+#RUN apk add --no-cache musl-dev
+#
+#WORKDIR /app
+#
+#COPY ./ /app
+#
+#RUN cargo build --release
+#