Vercel-update-docs: Turn "document synchronization" from verbal agreement into engineering process

Out of sync between code and documentation is probably the most common chronic disease in open source projects. The API signature has been changed, but the documentation is still as old as three months ago; new props have been added to the component, but the example code is still old. Small projects can rely on the maintainer's good memory, but a warehouse like Next.js with thousands of files will collapse long ago if it relies on memory. Vercel’s approach is to plug this process into Agent. The .agents/skills directory of the next.js warehouse maintains an official skill called update-docs. When the maintainer reviews the PR, let AI follow the code changes to find the affected documents, confirm the modifications one by one, and even build the document skeleton of the new function from scratch. This skill is bigger than others on the market