Update planner creation instructions. (#29)

(https://github.com/CodeYourFuture/My-Coursework-Planner/commit/a708cc854c2897d19e7950ccb8c6ddbbb89affcc)
This addresses the issues raised in [this issue](https://github.com/CodeYourFuture/CYF-PD/issues/142) by updating the setup instructions to specify the name of the board trainees create. It also removes references to the kamino clone extension and redirects trainees to Slack/study groups for help.

首先查看 planner 的设置说明以及所引用的提交 a708cc854c2897d19e7950ccb8c6ddbbb89affcc。说明中指定 board 名称、移除对 Kamino clone extension 的引用，并指导 trainees 在 Slack 或 study groups 中寻求帮助，即表示完成。

由索引模型根据 Issue 内容生成。