docs(getting-started): static files on CF Workers

[stukennedy]

there is a requirement to add a manifest to the serveStatic adapter method, the docs correctly shows that you need to import a manifest from the special __STATIC_CONTENT_MANIFEST module

However, this results in a Typescript error, as this module is generated by wrangler. This change to the docs explains how the user can add a type definition so that the error goes away, otherwise they may assume that the example is incorrect.

[yusukebe]

Hi @stukennedy

Thanks! That's a good suggestion. I've left the comments. Please check them.