[css-text] Add example for arbitrary breaking of Arabic text.

Author: fantasai

css-text/Overview.bs

@@ -922,6 +922,12 @@ Line Breaking Details</h3>
       due to ''break-all'', the characters must still be shaped as if the
       word were not broken.</p>
 
+    <div class="example">
+      For example, if the word “نوشتن” is broken between the “ش” and “ت”,
+      the “ش” still takes its initial form (“ﺷ”), and the “ت” its medial form (“ﺘ”),
+      as in “ﻧﻮﺷﺘﻦ”.
+    </div>
+
   <h3 id="line-break-property">
     Breaking Rules for Punctuation: the 'line-break' property</h3>