Create fieldApi.md

Author: tannerlinsley

docs/framework/react/reference/fieldApi.md

@@ -0,0 +1,13 @@
+---
+id: fieldApi
+title: Field API
+---
+
+### `FieldApi<TData, TFormData>`
+
+When using `@tanstack/react-form`, the [core field API](../../reference/fieldApi) is extended with additional methods for React-specific functionality:
+
+- ```tsx
+  Field: FieldComponent<TData, TFormData>
+  ```
+  - A pre-bound and type-safe sub-field component using this field as a root.