docs: function validateConfig (config) {
    const customJoi = Joi.extend((joi) => ({
      base: joi.string(),
      name: 'file',
      language: {
        exists: 'file or directory must exists',
      },
      rules: [
        {
          name: 'exists',
          validate(params, value, state, options) {
            if (!fs.existsSync(value)) {
              return this.createError('file.exists', { v: value }, state, options)
            }
            return value
          }
        }
      ]
    }))
  
    const schema = Joi.object().keys({
      content: customJoi.file().exists().required(),
      output: Joi.string().required(),
      include: Joi.array().min(1).items(Joi.string()).required(),
      exclude: Joi.array().min(1).items(Joi.string()).required(),
      contentTypes: Joi.array().min(1).items(Joi.object()).required(),
    })
    const result = Joi.validate(config, schema, (err, value) => {
      if (err !== null) {
        throw err
      }
    })
  }