doc/tutorial/basics: add test for tutorial

test whether examples in tutorial produce the desired
results.

Closes #50.

Change-Id: I3c5b8a465e6ed98dad2962efd88ce246173250a6
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2178
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/doc/tutorial/basics/rangedef.md b/doc/tutorial/basics/rangedef.md
index 4c49c6a..d0939c3 100644
--- a/doc/tutorial/basics/rangedef.md
+++ b/doc/tutorial/basics/rangedef.md
@@ -43,7 +43,7 @@
 <!-- result -->
 `$ cue eval -i range.cue`
 ```
-a: _|_
+a: _|_ /* -1 not within bound int & >=0 */
 b: 128
 c: 2000000000
 ```
\ No newline at end of file