README.md

@@ -88,6 +88,14 @@ Only types supported in the kernel can be referenced.
   does not fit into int32, it would raise an error. (Issue #2)
 * Only `uint32`, `int32` (and range of them) can be used as index.
 
+### Kernel Only class
+* Annotate the class with `@kernel`.
+* Functions are all kernel only, including constructor.
+
+Questions:
+* Should we also do `@portable`?
+* Support inheritance and polymorphism?
+
 ## Generics
 We use [type variable](https://docs.python.org/3/library/typing.html#typing.TypeVar) for denoting generics.