Update EE > CE downgrade service removal steps

doc/downgrade_ee_to_ce/README.md

@@ -15,9 +15,9 @@ Kerberos and Atlassian Crowd are only available on the Enterprise Edition, so
 you should disable these mechanisms before downgrading and you should provide
 alternative authentication methods to your users.
 
-### Remove Jenkins CI Service entries from the database
+### Remove Service Integration entries from the database
 
-The `JenkinsService` class is only available on the Enterprise Edition codebase,
+The `JenkinsService` and `GithubService` classes are only available in the Enterprise Edition codebase,
 so if you downgrade to the Community Edition, you'll come across the following
 error:
 
@@ -30,20 +30,31 @@ column if you didn't intend it to be used for storing the inheritance class or o
 use another column for that information.)
 ```
 
+or
+
+```
+Completed 500 Internal Server Error in 497ms (ActiveRecord: 32.2ms)
+
+ActionView::Template::Error (The single-table inheritance mechanism failed to locate the subclass: 'GithubService'. This
+error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this
+column if you didn't intend it to be used for storing the inheritance class or overwrite Service.inheritance_column to
+use another column for that information.)
+```
+
 All services are created automatically for every project you have, so in order
 to avoid getting this error, you need to remove all instances of the
-`JenkinsService` from your database:
+`JenkinsService` and `GithubService` from your database:
 
 **Omnibus Installation**
 
 ```
-$ sudo gitlab-rails runner "Service.where(type: ['JenkinsService', 'JenkinsDeprecatedService']).delete_all"
+$ sudo gitlab-rails runner "Service.where(type: ['JenkinsService', 'JenkinsDeprecatedService', 'GithubService']).delete_all"
 ```
 
 **Source Installation**
 
 ```
-$ bundle exec rails runner "Service.where(type: ['JenkinsService', 'JenkinsDeprecatedService']).delete_all" production
+$ bundle exec rails runner "Service.where(type: ['JenkinsService', 'JenkinsDeprecatedService', 'GithubService']).delete_all" production
 ```
 
 ### Secret variables environment scopes