Add metadata for whether a library has TypeScript types

[brentvatne]

Should we differentiate between libraries that have "typings" and those that are written in TypeScript? Does that matter?

TODO

• Add to schema and README
• Maybe add a filter?
• Display in the library UI

[mrousavy]

Well it would be useful to know if there are types in the DefinitelyTyped repository which have to be extra installed as a dev dependency (npm i @types/react-native-some-library -D), or if the types are already inside the library (.d.ts).