add dockerfile

dockerfile

@@ -0,0 +1,16 @@
+FROM golang:1.23.1-alpine3.20 as build
+
+COPY . /src
+
+RUN cd /src \
+    && go build -o downloadhub \
+    && mkdir -p ./fs/var/opt/downloadhub \
+    && mkdir -p ./fs/opt/downloadhub \
+    && cp downloadhub ./fs/opt/downloadhub/downloadhub
+
+FROM scratch as prod
+
+COPY --from=build --chmod=755 /src/fs /
+
+EXPOSE 8080
+ENTRYPOINT [ "/opt/downloadhub/downloadhub", "-c", "/var/opt/downloadhub/content.json" ]