📝 caveat when upgrading to worker 0.0.18 (#400)

README.md

@@ -424,6 +424,19 @@ please [take a look](https://www.cloudflare.com/careers/).
   your code depends on, or strip as much from the `.wasm` binary as possible. Here are some extra
   steps you can try: https://rustwasm.github.io/book/reference/code-size.html#optimizing-builds-for-code-size
 
+### ⚠️ Caveats
+
+1. Upgrading worker package to version `0.0.18` and higher
+
+- While upgrading your worker to version `0.0.18` an error `error[E0432]: unresolved import `crate::sys::IoSourceState` can appear.
+  In this case, upgrade `package.edition` to `edition = "2021"` in `wrangler.toml`
+
+```toml
+[package]
+edition = "2021"
+```
+
+
 # Contributing
 
 Your feedback is welcome and appreciated! Please use the issue tracker to talk about potential