Updating documentation to include a missing step in the update procedure

doc/update/8.2-to-8.3.md

@@ -120,6 +120,14 @@ There are new configuration options available for [`gitlab.yml`][yaml]. View the
 git diff origin/8-2-stable:config/gitlab.yml.example origin/8-3-stable:config/gitlab.yml.example
 ```
 
+#### GitLab default file
+
+The value of the `gitlab_workhorse_options` variable should be updated within the default gitlab file (`/etc/default/gitlab`) according to the following diff:
+
+```sh
+git diff origin/8-2-stable:lib/support/init.d/gitlab.default.example origin/8-3-stable:lib/support/init.d/gitlab.default.example
+```
+
 #### Nginx configuration
 
 GitLab 8.3 introduces major changes in the NGINX configuration.