_content/doc/tutorial/fuzz: add note about combining characters in example

Currently, the fuzzing tutorial provides a reverse function to use.
This led to some confusion on if it is production ready, which it is not.
Adds a note that the code does not handle combining characters correctly.

Fixes golang/go#69628

Change-Id: Id0f3a5699417d9249dc7061ff126aef15872cc83
GitHub-Last-Rev: 44c70a6aab2a61639a26fce28ce406475d821641
GitHub-Pull-Request: golang/website#305
Reviewed-on: https://go-review.googlesource.com/c/website/+/639216
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

_content/doc/tutorial/fuzz.md

diff --git a/_content/doc/tutorial/fuzz.md b/_content/doc/tutorial/fuzz.md
index 881ba8f..f3916fe 100644
--- a/_content/doc/tutorial/fuzz.md
+++ b/_content/doc/tutorial/fuzz.md
@@ -465,7 +465,8 @@
 ```
 
 The key difference is that `Reverse` is now iterating over each `rune` in the
-string, rather than each `byte`.
+string, rather than each `byte`. Note that this is just an example, and does not
+handle [combining characters](https://en.wikipedia.org/wiki/Combining_character) correctly.
 
 #### Run the code