doc: links to schema docs from doc readme index.
- cids are links
- linkloader and linkbuilder
- automatical link loading in operationals
+- [IPLD Schemas](./schema.md)
+ - [Goals](./schema.md#goals)
+ - [Features](./schema.md#features)
+ - [Implementation](./schema.md#implementation)
+ - [Migration Techniques](./schema.md#schemas-and-migration)
