message: docs: update README.md on the root package
diff: # js-sdk
  +
  +This repository is a monorepo for kintone development!
  +
  +## packages
  +
  +| Name | Description | Links |
  +| ------------------ | :-----------------------------------------------: | :------: |
  +| [@kintone/rest-api-client](https://github.com/kintone/js-sdk/tree/master/packages/rest-api-client) | A API client for kintone REST API | [![npm version](https://badge.fury.io/js/%40kintone%2Frest-api-client.svg)](https://badge.fury.io/js/%40kintone%2Frest-api-client)
  