added dockerfile

dockerfile

@@ -0,0 +1,13 @@
+FROM node:latest
+WORKDIR /app
+
+COPY ./index.html .
+COPY ./main.js .
+COPY ./backend.js .
+COPY ./package.json ./package-lock.json .
+
+RUN npm ci --only=production
+
+EXPOSE 3000
+CMD ["npm" "backend.js"]
+