[css-text-4] Add issue link for French punctuation spacing fixup.

Author: fantasai

css-text-4/Overview.bs

@@ -991,6 +991,9 @@ Character Class Spacing: the 'text-spacing' property</h3>
 			Otherwise this value has no effect.
 			However future specifications may add automatic spacing behavior for other languages.
 
+			ISSUE: Integrate rules for correcting incorrect spaces?
+			<a href="https://github.com/w3c/csswg-drafts/issues/318">Issue 318</a>
+
 		<dt><dfn>space-start</dfn>
 		<dd>
 			Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)