Add Dockerfile

Dockerfile initially proposed by @gyscos at #880

contrib/docker/Dockerfile

@@ -0,0 +1,20 @@
+# Dockerfile
+# First image to build the binary
+FROM alpine as builder
+
+RUN apk --no-cache add make gcc libc-dev
+COPY . /src
+RUN mkdir /pkg && cd /src && make && make DESTDIR=/pkg install
+
+# Second minimal image to only keep the built binary
+FROM alpine
+
+# Copy the built files
+COPY --from=builder /pkg /
+
+# Copy the license as well
+RUN mkdir -p /usr/local/share/licenses/zstd
+COPY --from=builder /src/LICENSE /usr/local/share/licences/zstd/
+
+# Just run `zstd` if no other command is given
+CMD ["/usr/local/bin/zstd"]