Update README.md

Author: swhitty

README.md

@@ -34,7 +34,7 @@ This allows actors to synchronously start continuations and mutate their isolate
 
 ```swift
 let val: String = await withIdentifiableContinuation(isolation: self) {
-  // executed within actor isolation so can immediatley mutate actor state
+  // executed within actor isolation so can immediately mutate actor state
   continuations[$0.id] = $0
 } onCancel: { id in
   // @Sendable closure executed outside of actor isolation requires `await` to mutate actor state