Add missing what's new page

And link to it from version independent guide.

lib/tasks/versions.rake

@@ -28,6 +28,8 @@ namespace :versions do
       latest_man = "source/#{url}"
       FileUtils.ln_sf Pathname.new(file).relative_path_from(File.dirname(latest_man)), latest_man
     end
+    puts "Updating whats_new symlink..."
+    FileUtils.ln_sf Pathname.new("#{succ_root}/whats_new.html.md").relative_path_from("source"), "source/whats_new.html.md"
   end
 end
 

source/guides/getting_started.html.md

@@ -10,7 +10,7 @@ Bundler is an exit from dependency hell, and ensures that the gems
 you need are present in development, staging, and production.
 Starting work on a project is as simple as `bundle install`.
 
-<a href="../v2.4/whats_new.html" class="btn btn-primary">What's new in Bundler</a>
+<a href="../whats_new.html" class="btn btn-primary">What's new in Bundler</a>
 <a href="./rationale.html" class="btn btn-primary">Why Bundler exists</a>
 
 ## Getting Started

source/whats_new.html.md

@@ -0,0 +1 @@
+../v2.6/whats_new.html.md