Add note on Asana tokens to 8.3 update guide

[ci skip]

doc/update/8.2-to-8.3.md

@@ -179,6 +179,21 @@ To make sure you didn't miss anything run a more thorough check:
 
 If all items are green, then congratulations, the upgrade is complete!
 
+### 11. Update Asana Tokens
+
+[Asana API Keys have been deprecated](https://asana.com/developers/feed/api-key-deprecation)
+in favor of Personal Access Tokens and OAuth. You can create a personal access
+token for GitLab on [the Apps tab of your profile settings](https://app.asana.com/-/account_api).
+
+Once you have a token, you can update all projects via the console:
+
+```ruby
+AsanaService.all.each { |s| s.api_key = '[PERSONAL_ACCESS_TOKEN]'; s.save }
+```
+
+See [#2111](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2111) for
+more details on this change.
+
 ## Things went south? Revert to previous version (8.2)
 
 ### 1. Revert the code to the previous version