def app_yaml_exists?
      if @site.respond_to?(:in_source_dir)
        File.exists? @site.in_source_dir("app.yaml")
      else
        File.exists? Jekyll.sanitized_path(@site.source, "app.yaml")
      end
    end
def app_yaml_exists?
      if @site.respond_to?(:in_source_dir)
        File.exists? @site.in_source_dir("app.yaml")
      else
        File.exists? Jekyll.sanitized_path(@site.source, "app.yaml")
      end
    end
Checks if a app.yaml already exists in the site source