Update gitlab_rails_cheat_sheet.md

There is no example of the rails runner which demonstrates that you will need to use something like puts to actually print the personal_access_token.token 

Since the only example at the top is the runner, if you try the example generation of a personal access token. It will create the token, but not return the value. So you can't use it.

doc/administration/troubleshooting/gitlab_rails_cheat_sheet.md

@@ -442,7 +442,7 @@ personal_access_token = User.find(123).personal_access_tokens.create(
   scopes: [:api]
 )
 
-personal_access_token.token
+puts personal_access_token.token
 ```
 
 You might also want to manually set the token string: