code: func initLessons(tmpl *template.Template, content string) error {
  	dir, err := os.Open(content)
  	if err != nil {
  		return err
  	}
  	files, err := dir.Readdirnames(0)
  	if err != nil {
  		return err
  	}
  	for _, f := range files {
  		if filepath.Ext(f) != ".article" {
  			continue
  		}
  		content, err := parseLesson(tmpl, filepath.Join(content, f))
  		if err != nil {
  			return fmt.Errorf("parsing %v: %v", f, err)
  		}
  		name := strings.TrimSuffix(f, ".article")
  		lessons[name] = content
  	}
  	return nil
  }
docs: // initLessonss finds all the lessons in the passed directory, renders them,
  // using the given template and saves the content in the lessons map.