feature: add Dockerfile & docker-compose installation instructions

Dockerfile

@@ -0,0 +1,18 @@
+FROM node:14.5-alpine as frontend
+RUN apk --no-cache add curl
+WORKDIR /usr/src/app
+COPY frontend .
+RUN yarn install
+RUN yarn build
+
+FROM golang:1.14.5-alpine as backend
+WORKDIR /usr/src/app
+COPY . .
+COPY --from=frontend /usr/src/app/build .
+RUN go run cmd/mage/main.go backend:genFrontend backend:build
+
+FROM alpine:latest
+WORKDIR /root/
+COPY --from=backend /usr/src/app/dist/citadel .
+COPY --from=backend /usr/src/app/conf/app.example.toml conf/app.toml
+CMD ["./citadel", "web"]