Add rails:update to the upgrading guides

[ci skip]

1 files changed, 23 insertions, 0 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 6800e71a3c..6260b39f5c 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -22,6 +22,29 @@ Rails generally stays close to the latest released Ruby version when it's releas
 
 TIP: Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails. Ruby Enterprise Edition has these fixed since the release of 1.8.7-2010.02. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x, jump straight to 1.9.3 for smooth sailing.
 
+### The Rake Task
+
+Rails provides the `rails:update` rake task. After updating the Rails version
+in the Gemfile, run this rake task.
+This will help you with the creation of new files and changes of old files in a
+interactive session.
+
+```bash
+$ rake rails:update
+   identical  config/boot.rb
+       exist  config
+    conflict  config/routes.rb
+Overwrite /myapp/config/routes.rb? (enter "h" for help) [Ynaqdh]
+       force  config/routes.rb
+    conflict  config/application.rb
+Overwrite /myapp/config/application.rb? (enter "h" for help) [Ynaqdh]
+       force  config/application.rb
+    conflict  config/environment.rb
+...
+```
+
+Don't forget to review the difference, to see if there were any unexpected changes.
+
 Upgrading from Rails 4.1 to Rails 4.2
 -------------------------------------