[css-text] Clarify what inline means. Fixes w3c#579

Author: fantasai

css-text/Overview.bs

@@ -1323,7 +1323,7 @@ Line Breaking Details</h3>
     Name: text-justify
     Value: auto | none | inter-word | inter-character
     Initial: auto
-    Applies to: inlines
+    Applies to: <a>inline boxes</a>
     Inherited: yes
     Canonical order: n/a
     </pre>