link directly to new supplemental guidance (#2296)

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---------

Co-authored-by: Mike Gower <mikegower@gmail.com>
Co-authored-by: Kenneth G. Franqueiro <kfranqueiro@users.noreply.github.com>
(cherry picked from commit 80ba129)

Author: 3 people

guidelines/index.html

@@ -28,7 +28,7 @@ <h3>Background on WCAG 2</h3>
 				<p>Web Content Accessibility Guidelines (WCAG) 2.1 defines how to make web content more accessible to people with disabilities. Accessibility involves a wide range of disabilities, including visual, auditory, physical, speech, cognitive, language, learning, and neurological disabilities. Although these guidelines cover a wide range of issues, they are not able to address the needs of people with all types, degrees, and combinations of disability. These guidelines also make web content more usable by older individuals with changing abilities due to aging and often improve usability for users in general.</p>
 				<p>WCAG 2.1 is developed through the <a href="https://www.w3.org/WAI/standards-guidelines/w3c-process/">W3C process</a> in cooperation with individuals and organizations around the world, with a goal of providing a shared standard for web content accessibility that meets the needs of individuals, organizations, and governments internationally. WCAG 2.1 builds on WCAG 2.0 [[WCAG20]], which in turn built on WCAG 1.0 [[WAI-WEBCONTENT]] and is designed to apply broadly to different web technologies now and in the future, and to be testable with a combination of automated testing and human evaluation. For an introduction to WCAG, see the <a href="https://www.w3.org/WAI/standards-guidelines/wcag/">Web Content Accessibility Guidelines (WCAG) Overview</a>.</p>
 
-				<p>Significant challenges were encountered in defining additional criteria to address cognitive, language, and learning disabilities, including a short timeline for development as well as challenges in reaching consensus on testability, implementability, and international considerations of proposals. Work will carry on in this area in future versions of WCAG. We encourage authors to refer to our supplemental guidance on <a href="https://www.w3.org/WAI/standards-guidelines/wcag/#supplement">improving inclusion for people with disabilities, including learning and cognitive disabilities, people with low-vision, and more</a>.</p>
+				<p>Significant challenges were encountered in defining additional criteria to address cognitive, language, and learning disabilities, including a short timeline for development as well as challenges in reaching consensus on testability, implementability, and international considerations of proposals. Work will carry on in this area in future versions of WCAG. We encourage authors to refer to our <a href="https://www.w3.org/WAI/WCAG2/supplemental/about/">supplemental guidance on improving inclusion</a> for people with disabilities, including cognitive and learning disabilities, low vision, and more.</p>
 
 				<p>Web accessibility depends not only on accessible content but also on accessible web browsers and other user agents. Authoring tools also have an important role in web accessibility. For an overview of how these components of web development and interaction work together, see:</p>
 				<ul>