Parallelly familiarize yourself with unfamiliar codebase and generate onboarding documentation using codebase-onboarding

### 翻译结果： This article introduces the `codebase-onboarding` skill in spencerpauly/awesome-cursor-skills: it launches 5 read-only explore sub-agents in parallel to research architecture, data models, APIs, authentication and deployment respectively, then synthesizes the results into an ONBOARDING.md. Based on the official SKILL.md and Cursor Skills documentation, it explains the installation directory, the `npx skills` installation method, the calling mode of `/codebase-onboarding`, as well as applicable scenarios and review precautions.