Merge branch 'update-cookbook-version-8.1' into 'develop'

Update Documentation/Cookbook/_static/html/versions.html 8.1

See merge request !930

Documentation/Cookbook/_static/html/versions.html

@@ -16,6 +16,7 @@
             <dd><a href="https://www.orfeo-toolbox.org/CookBook-7.3/">7.3.0</a></dd>
             <dd><a href="https://www.orfeo-toolbox.org/CookBook-7.4/">7.4.0</a></dd>
             <dd><a href="https://www.orfeo-toolbox.org/CookBook-8.0/">8.0.1</a></dd>
+            <dd><a href="https://www.orfeo-toolbox.org/CookBook-8.1/">8.1.0</a></dd>
             <dd><a href="https://www.orfeo-toolbox.org/CookBook-develop/">develop</a></dd>
         </dl>
     </div>