Fix 18009: add missing steps in update docs

doc/update/8.6-to-8.7.md

@@ -86,6 +86,14 @@ sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS
 
 ### 7. Update configuration files
 
+#### New configuration options for `gitlab.yml`
+
+There are new configuration options available for [`gitlab.yml`](config/gitlab.yml.example). View them with the command below and apply them manually to your current `gitlab.yml`:
+
+```sh
+git diff origin/8-6-stable:config/gitlab.yml.example origin/8-7-stable:config/gitlab.yml.example
+```
+
 #### Git configuration
 
 Disable `git gc --auto` because GitLab runs `git gc` for us already.

doc/update/8.7-to-8.8.md

@@ -86,6 +86,14 @@ sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS
 
 ### 7. Update configuration files
 
+#### New configuration options for `gitlab.yml`
+
+There are new configuration options available for [`gitlab.yml`](config/gitlab.yml.example). View them with the command below and apply them manually to your current `gitlab.yml`:
+
+```sh
+git diff origin/8-7-stable:config/gitlab.yml.example origin/8-8-stable:config/gitlab.yml.example
+```
+
 #### Git configuration
 
 Disable `git gc --auto` because GitLab runs `git gc` for us already.
@@ -137,7 +145,7 @@ To make sure you didn't miss anything run a more thorough check:
 
 If all items are green, then congratulations, the upgrade is complete!
 
-## Things went south? Revert to previous version (8.6)
+## Things went south? Revert to previous version (8.7)
 
 ### 1. Revert the code to the previous version