Added 2-staged dockerfile

ref #2

Dockerfile

@@ -3,3 +3,10 @@ WORKDIR /app
 COPY . .
 RUN yarn
 RUN yarn build
+
+# final image
+FROM alpine
+COPY --from=0 /app/dist /app
+FROM fholzer/nginx-brotli:v1.19.1
+COPY --from=1 /app /usr/share/nginx/html
+COPY ./nginx.conf /etc/nginx/nginx.conf