[css-fonts-4] [varfont] Add an example of optical sizing

Thanks to Nick Sherman for his generous permission to let us use his fantastic example.

Author: litherum

css-fonts-4/Century_Expanded-a-normalized.jpg

@@ -1170,7 +1170,7 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 
 	Note: Some user operations, such as pinch-zoom, may be considered not-layout-causing if they do not cause text to reflow. However, other user operations, such as increasing text size for accessiblity purposes, may be considered layout-causing because they cause text to reflow. Similarly, the 'transform' property may be considered not-layout-causing because transforms generally do not cause text to reflow. Each user-agent is free to decide whether or not each operation is layout-changing or not.
 
-	<div class="figure"><img alt="text with and without 'font-optical-sizing'" src="fontopticalsize.png" /><p class="caption">Text with and without the use of 'font-optical-sizing'</p></div>
+	<div id="optical-size-example" class="figure"><img alt="text with different optical sizes, normalized to similar physical sizes" src="Century_Expanded-a-normalized.jpg" /><p class="caption">Each size of Century Expanded as it existed in analog metal form. The different optical sizes, normalized here to the same physical size, have design variations to maintain stylistic traits and improve readability.</p></div>
 
 <h3>Low-level font variation settings control: the 'font-variation-settings' property</h3>
 
@@ -1319,7 +1319,10 @@ an emoji font or not, UTR51 defines a the default behavior for a given codepoint
 
 <p class="example">Example of author control over emoji/text styles</p>
 
-<h2 class="no-num" id="acknowledgments">Acknowledgments</h2>
+<h2 id="acknowledgments">Acknowledgments</h2>
+
+	The CSS Working Group would like to thank <a href="http://nicksherman.com">Nick Sherman</a>, for his generous permission to use the above <a href="#optical-size-example">example</a> of optical sizing.
+
 
 <script>
 if ('ontouchstart' in window || navigator.maxTouchPoints > 0 || navigator.msMaxTouchPoints > 0) {