Improve "Best Practices" regarding NODE_ENV

Problem

I just spent half a day trying to figure out, why trying to build an Angular project in Docker failed. I've followed the advice at Best Practices, not aware, that setting NODE_ENV to production causes npm not to install devDependencies.

Solution

The Best Practices guide should differentiate between using Node.js to build a Node.js based project (NODE_ENV=development) and to run a Node.js based project (NODE_ENV=production). Both can even be combined using multi-stage builds.

从 docs/BestPractices.md 中链接的部分开始，查看其中如何描述 Docker 构建期间和运行时的 NODE_ENV。更新指南以区分开发构建和生产运行，并说明 multi-stage 构建可以同时使用两者；文档应明确防止在构建期间省略 devDependencies。