docs(BestPractices.md): add dependency caching guide

To avoid performing npm install again and again when any source code in the project is being modified, it's (always?) preferred to cached node_modules as long as package.json and package-lock.json are not changed. I think this can be added to the BestPractices.md guide. Welcome for discussions on whether this is really a good practice also.

从 BestPractices.md 开始，检查现有的依赖安装和镜像构建指南。确认在 package.json 和 package-lock.json 未发生变化时缓存 node_modules 的预期做法，然后结合相关的 npm install 上下文对其进行记录。当指南清楚地说明缓存方法及其条件时，即视为完成。