docs: Clarify popstate handling in caching exercise

Author: Ala-Ben-Aissia

exercises/04.router/05.problem.cache/ui/index.js

@@ -54,12 +54,13 @@ function Root() {
 			setNextLocation(nextLocation)
 			// 🐨 get the historyKey from window.history.state?.key (or fallback to a new one with generateKey)
 
-			// 🐨 if the contentCache does not have an entry for the historyKey, then trigger this update:
+			// 🐨 if the contentCache has an entry for the historyKey, then setContentKey(historyKey) directly.
+			//    (⚠️ no startTransition needed here because the content is already available).
+			// 🐨 otherwise, fetch new content and wrap the update in startTransition:
 			const fetchPromise = fetchContent(nextLocation)
 			const nextContentPromise = createFromFetch(fetchPromise)
 			// 🐨 use the historyKey to add the nextContentPromise in the contentCache
-
-			// 🐨 change this to setContentKey(historyKey)
+			// 🐨 and change this to setContentKey(historyKey)
 			startTransition(() => setContentPromise(nextContentPromise))
 		}
 		window.addEventListener('popstate', handlePopState)