Try to report where the file should be

app/services/ci/create_pipeline_service.rb

@@ -33,7 +33,7 @@ module Ci
 
       unless pipeline.config_processor
         unless pipeline.ci_yaml_file
-          return error('Missing .gitlab-ci.yml file')
+          return error("Missing #{pipeline.ci_yaml_file_path} file")
         end
         return error(pipeline.yaml_errors, save: save_on_errors)
       end