Add issue about atomic inlines and letter-spacing

Author: fantasai

css3-text/Overview.src.html

@@ -2305,6 +2305,8 @@ <h3 id="letter-spacing">
        and rendered within the innermost element that <em>contains</em>
        the boundary.</p>
 
+    <p class="issue">How are atomic inlines handled wrt letter-spacing?</p>
+
     <div class="example">
       <p>For example, given the markup</p>