add link to scaling rate issue

Author: davidsgrogan

css-fonts-5/Overview.bs

@@ -84,6 +84,8 @@ is recognized as setting the computed value
 of the ''font-size/medium'' font size
 and consequently scaling the computed size of the other <<absolute-size>> keywords.
 
+Issue(12475):
+
 The value of the <code>content</code>
 attribute must be an <a>ASCII case-insensitive</a> match for one of the
 recognized keywords. Otherwise the tag is ignored.