improve instructions

Author: kentcdodds

exercises/01.discovery/01.problem.cors/README.mdx

@@ -86,3 +86,5 @@ export default {
 👨‍💼 Thanks Kellie! Let's take a look at that.
 
 Now, start by understanding why CORS matters for MCP servers, implement the solution using the provided utility, and test that cross-origin requests work properly.
+
+You'll know it's working when you try to run the OAuth flow in the MCP Inspector and you no longer get CORS errors in the network tab of your dev tools. Instead you'll get 404 errors instead and we'll deal with those in the next step.