message: docs: add a link to CONTRIBUTING.md
diff: @@ -7,3 +7,8 @@ This repository is a monorepo for kintone development!
  | 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)
  +
  +## Contribution Guide
  +
  +- [CONTRIBUTING.md](https://github.com/kintone/js-sdk/blob/master/CONTRIBUTING.md)
  +
  