[css-text-3] Link to i18n typography index from intro.

Author: fantasai

css-text-3/Overview.bs

@@ -126,6 +126,12 @@ Introduction</h2>
     <a href="https://www.w3.org/TR/css3-writing-modes/">CSS Writing Modes Level 3</a> [[CSS3-WRITING-MODES]].
   </div>
 
+  Further information about the typesetting requirements
+  of various languages and writing systems around the world
+  can be found in the <a href="https://www.w3.org/International/core/">Internationalization Working Group</a>’s
+  <a href="https://www.w3.org/TR/typography/">Typography Index</a>.
+  [[TYPOGRAPHY]]
+
 <h3 id="placement">
 Module Interactions</h3>