Merge pull request #32596 from bogdanvlviv/add-reference-to-5_2-from-edge-guides

Add the reference to Rails Guides 5.2 from the Edge Guides

guides/source/_welcome.html.erb

@@ -16,6 +16,7 @@
 <% end %>
 <p>
 The guides for earlier releases:
+<a href="http://guides.rubyonrails.org/v5.2/">Rails 5.2</a>,
 <a href="http://guides.rubyonrails.org/v5.1/">Rails 5.1</a>,
 <a href="http://guides.rubyonrails.org/v5.0/">Rails 5.0</a>,
 <a href="http://guides.rubyonrails.org/v4.2/">Rails 4.2</a>,