content: add Arabic to the list of available languages

Add Arabic to the list of languages available.

Change-Id: I61f7dffc92cb70f9c436ac7b3ff6243d3c695e44
GitHub-Last-Rev: 3574b0b84e9e0236833518840f393bb817a1e1ca
GitHub-Pull-Request: golang/tour#862
Reviewed-on: https://go-review.googlesource.com/c/tour/+/209958
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
diff --git a/content/welcome.article b/content/welcome.article
index 3e0b595..51aa919 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -47,6 +47,7 @@
 
 The tour is available in other languages:
 
+- [[https://go-tour-ar.appspot.com/][Arabic — العربية]]
 - [[https://go-tour-br.appspot.com/][Brazilian Portuguese — Português do Brasil]]
 - [[https://go-tour-ca.appspot.com/][Catalan — Català]]
 - [[https://tour.go-zh.org/][Simplified Chinese — 中文(简体)]]