docs(editor): add typedoc for schema module (#12830)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Documentation**
- Added comprehensive documentation for the `Schema` class, detailing
its methods, properties, and usage.
- Improved formatting and linking in the documentation for the `Store`
class, enhancing clarity and navigation.
- Updated the README to include a direct link to the new `Schema` class
documentation.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/docs/api/@blocksuite/store/classes/Store.md

@@ -1035,13 +1035,13 @@ Get the Doc instance for current store.
 
 #### Get Signature
 
-> **get** **schema**(): `Schema`
+> **get** **schema**(): [`Schema`](Schema.md)
 
-Get the Schema instance of the store.
+Get the [Schema](Schema.md) instance of the store.
 
 ##### Returns
 
-`Schema`
+[`Schema`](Schema.md)
 
 ***