Add a Dockerfile for container-ized web hosting

Dockerfile

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+FROM rust:1.89 AS builder
+
+RUN apt-get update
+RUN apt-get install -y --no-install-recommends libasound2-dev libudev-dev
+RUN rustup target add wasm32-unknown-unknown
+RUN cargo install --locked wasm-bindgen-cli
+
+# Copy in only the parts we care about. This is to prevent Docker from re-
+# running some steps because unimportant files changed (e.g.: the .git/ folder)
+COPY src/ ./src
+COPY Cargo.toml ./Cargo.toml
+# WARN: The lockfile doesn't exist in the repo. You will have to create it
+# before building the Docker image (i.e.: run `cargo update` first)
+COPY Cargo.lock ./Cargo.lock
+COPY www/ ./www
+COPY Makefile ./Makefile
+
+# Oops. There's no text output in the Docker build command line (it still works, though)
+RUN make
+
+FROM busybox:musl
+RUN mkdir -p /var/www
+COPY --from=builder ./out/ /var/www
+WORKDIR /var/www
+
+# TODO: Make httpd accept interrupt signals so the container exits properly.
+# (<ctrl>+c and `docker stop ...` don't work because Busybox doesn't answer)
+CMD ["httpd", "-f", "-p", "8080"]