add docker file

Dockerfile

@@ -0,0 +1,15 @@
+FROM golang:1.12-alpine AS builder
+WORKDIR /src
+COPY . .
+RUN \
+    apk add taglib-dev sqlite build-base git && \
+    ./_do_build_server && \
+    ./_do_build_scanner && \
+    apk del build-base && \
+    mv ./gonic ./gonicscan /bin/
+VOLUME ["/data", "/music"]
+EXPOSE 80
+ENV GONIC_LISTEN_ADDR :80
+ENV GONIC_DB_PATH /data/gonic.db
+ENV GONIC_MUSIC_PATH /music
+CMD ["gonic"]