Add the link to v7.2 guide [ci-skip]

Author: y-yagi

guides/source/_welcome.html.erb

@@ -16,6 +16,7 @@
 <% end %>
 <p>
 The guides for earlier releases:
+<a href="https://guides.rubyonrails.org/v7.2/" data-turbo="false">Rails 7.2</a>,
 <a href="https://guides.rubyonrails.org/v7.1/" data-turbo="false">Rails 7.1</a>,
 <a href="https://guides.rubyonrails.org/v7.0/" data-turbo="false">Rails 7.0</a>,
 <a href="https://guides.rubyonrails.org/v6.1/" data-turbo="false">Rails 6.1</a>,