Update MIGRATING.md

Author: swyxio

MIGRATING.md

@@ -54,11 +54,18 @@ module: {
 
 </details>
 
-## JSDoc (Not using TS)
+## JSDoc
 
 - https://github.com/Microsoft/TypeScript/wiki/JsDoc-support-in-JavaScript
 - webpack's codebase uses JSDoc with linting by TS https://twitter.com/TheLarkInn/status/984479953927327744 (some crazy hack: https://twitter.com/thelarkinn/status/996475530944823296)
--
+
+Problems to be aware of:
+
+- `object` is converted to `any` for some reason.
+- If you have an error in the jsdoc, you get no warning/error. TS just silently doesn't type annotate the function.
+- [casting can be verbose](https://twitter.com/bahmutov/status/1089229349637754880)
+
+(*thanks [Gil Tayar](https://twitter.com/giltayar/status/1089228919260221441) and [Gleb Bahmutov](https://twitter.com/bahmutov/status/1089229196247908353) for sharing above commentary*)
 
 ## From JS