PW CU Article ref to Guides variant added

ofl/playwritecu/article/ARTICLE.en_us.html

@@ -13,6 +13,10 @@
 <p>
 	Playwrite Cuba is a variable font with a weight range from Thin (100) to
 	Regular (400), and supports over 150 Latin-based languages.
+	It has a single-weight sibling with Guides, 
+	<a href="https://fonts.google.com/specimen/Playwrite+CU+Guides">Playwrite CU Guides</a>, 
+	designed to harmonize seamlessly with this main font while providing a 
+	visual aid for primary school children.
 </p>
 <p>
 	To contribute, see