Readme tweak and router exercise tweak

Author: mattpocock

README.md

@@ -59,7 +59,7 @@ Exercises are in the [`./exercises`](./exercises) folder. They're designed to be
 Each exercise follows a similar pattern:
 
 - Look at the file with the `*.code.ts` extension. This gives you the code we're going to be working through and trying to understand.
-- Read through the `*.exercise.ts` file. Read through the file, comment-by-comment, and follow the instructions by **editing the file inline**.
+- Read through the `*.exercise.ts` file. Read through the file, comment-by-comment, and follow the instructions by either editing the file inline, or editing the `*.code.ts` file.
 - Wherever you see reference to `Solution #1`, check the `*.solutions.ts` file when you want to see the solution. **Make sure you check the solution before proceeding!** There's often crucial information there.
 
 Be careful to read through each part of the exercise carefully - if you skip over parts of them, it might get difficult to find your way back.

exercises/09-router.exercise.ts

@@ -77,8 +77,8 @@ routes.goTo("/dashboard", {
   something: "",
 });
 /**
- * 🕵️‍♂️ Investigate routes.goTo above. See if you notice all
- * of the cool bits of this API.
+ * 🕵️‍♂️ Investigate routes.goTo above. Discuss amongst yourselves to
+ * see if you can spot all of the ways that routes.goTo is type-safe.
  *
  * Solution #1
  */

exercises/09-router.solutions.ts

@@ -4,11 +4,25 @@
  * 💡 First, you can't pass an invalid route to the
  * first argument.
  *
+ * const routes = makeRouter({
+ *   "/": {},
+ * });
+ *
+ * routes.goTo("/users");
+ *             ^ ⛔️
+ *
  * Second, you get autocomplete on the search parameters
  * that you specify in the array in makeRoutes.
  *
- * Third, you can't pass a search parameter if the route
- * in question doesn't have a search: [].
+ * Third, you can't pass a second argument to routes.goTo at
+ * all if you haven't specified a search param on that route.
+ *
+ * const routes = makeRouter({
+ *   "/": {},
+ * });
+ *
+ * routes.goTo("/", {});
+ *                  ^ ⛔️
  *
  * #2
  *