Update broken link in tutorial docs README.md

https://cuelang.org/docs/tutorials/tour/ gives 404 and https://cuelang.org/docs/tutorials/tour/intro/ is valid link for tour homepage.

Closes #352
https://github.com/cuelang/cue/pull/352

GitOrigin-RevId: 14d7f704edb7258064c272c1190454d62d5600b8
Change-Id: If9170a947ef9fa239b0888c62d11700d45e0c4f5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5900
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/tutorial/basics/Readme.md b/doc/tutorial/basics/Readme.md
index 1fe53eb..a8a57b7 100644
--- a/doc/tutorial/basics/Readme.md
+++ b/doc/tutorial/basics/Readme.md
@@ -4,7 +4,7 @@
 
 The files in this directory are used to generate the tour in
 
-    https://cuelang.org/docs/tutorials/tour/
+    https://cuelang.org/docs/tutorials/tour/intro/
 
 They are kept here to ensure the examples are in sync with the latest update
 of CUE.