[css-inline] Add issue about which baselines need to be added/dropped.

Author: fantasai

css-inline/Overview.bs

@@ -30,6 +30,8 @@ At Risk: the 'initial-letter-wrap' property
 
 <p class="issue">This section is being rewritten. Refer to <a href="http://www.w3.org/TR/CSS21/visudet.html#line-height">section 10.8</a> of [[CSS21]] for the normative CSS definition or the <a href="http://www.w3.org/TR/2002/WD-css3-linebox-20020515/">2002 Working Draft</a> if you want pretty pictures. (But ignore the old text, half of it's wrong. We're not specifying which half, that's to be determined.)</p>
 
+Issue: The CSSWG would like to know which baseline values are necessary: if any can be dropped, or any need to be added.
+
 <h3 id="dominant-baseline property">
 Dominant Baselines: the 'dominant-baseline' property</h3>