content: add Thai translation of the tour.

Change-Id: If6746a57c6e44648a117d196af93e49da912675e
Reviewed-on: https://go-review.googlesource.com/52750
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/content/welcome.article b/content/welcome.article
index 72f35b3..f00d617 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -64,6 +64,7 @@
 - [[https://go-tour-uz.appspot.com/][Uzbek — Ўзбекча]]
 - [[https://go-tour-turkish.appspot.com/][Turkish - Türkçe]]
 - [[https://go-tour-ru-ru.appspot.com/][Russian - Русский]]
+- [[https://go-tour-th.appspot.com/][Thai - ภาษาไทย]]
 
 Click the [[javascript:highlightAndClick(".next-page")]["next"]] button or type `PageDown` to continue.