public static StepsRunner begin(BuildContext buildContext) {
    ExecutorService executorService =
        JibSystemProperties.serializeExecution()
            ? MoreExecutors.newDirectExecutorService()
            : buildContext.getExecutorService();

    return new StepsRunner(MoreExecutors.listeningDecorator(executorService), buildContext);
  }
Starts building the steps to run.

@param buildContext the {@link BuildContext}
@return a new {@link StepsRunner}
jib-core/src/main/java/com/google/cloud/tools/jib/builder/steps/StepsRunner.java