include Tibetan as a language option

The Tibetan alphabet was only recently included on Android, so the language
name needs to also have the English there.  Otherwise it'll appear blank
on devices without Tibetan.

app/src/main/res/values/settings_keys.xml

@@ -71,6 +71,7 @@
         <item>sl</item>
         <item>fi</item>
         <item>sv</item>
+        <item>bo</item>
         <item>vi</item>
         <item>tr</item>
         <item>bg</item>
@@ -149,6 +150,7 @@
         <item>Slovenščina</item>
         <item>Suomi</item>
         <item>Svenska</item>
+        <item>Tibetan བོད་སྐད།</item>
         <item>Tiếng Việt</item>
         <item>Türkçe</item>
         <item>Български</item>