Add Dockerfile.

Dockerfile

@@ -0,0 +1,25 @@
+FROM rust:1.64 as builder
+
+# Create a new empty project.
+RUN USER=root cargo new --bin tildes-statistics
+WORKDIR /tildes-statistics
+RUN mv src source
+
+# Copy the Cargo files and build in release, caching the dependencies.
+COPY Cargo.* .
+RUN cargo build --release
+
+# Then copy our code. This way when only the source code changes, the
+# dependencies don't have to be entirely rebuilt.
+COPY source source
+
+# Remove the cached tildes-statistics dependencies.
+RUN rm target/release/deps/tildes_statistics*
+
+# Build the executable with actual source code.
+RUN cargo install --path .
+
+# Copy the executable to a smaller final image.
+FROM debian:bullseye-slim
+COPY --from=builder /usr/local/cargo/bin/tildes-statistics /usr/local/bin
+CMD ["tildes-statistics"]