[FEAT] 배포를 위한 dockerfile 및 dockerignore 파일 추가

react-whenMeet/.dockerignore

+node_modules
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react-whenMeet/Dockerfile

+FROM node:20-alpine
+WORKDIR /app
+COPY package.json ./
+RUN npm install
+COPY . .
+EXPOSE 80
+CMD ["npm", "start"]
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