[css-fonts-5] Update acknowledgements.

Author: fantasai

css-fonts-5/Overview.bs

@@ -596,8 +596,15 @@ No new security or privacy considerations have been raised on this specification
 <h2 id="acknowledgments">
 Acknowledgments</h2>
 
-The CSS Working group would like to thank:
-
+	Firstly, the editors would like to thank all of the
+	<a href="https://www.w3.org/TR/css-fonts-4/#acknowledgments">contributors to the previous level of this module</a>.
+
+	Secondly, we would like to acknowledge
+	DerKoun from PDFReactor,
+	Xiaocheng Hu from Google,
+	and
+	Jonathan Kew from Mozilla,
+	for their contributions to the improvements in this Level 5.
 
 <h2 id="changes">
 Changes