add a tree component: he-tree-react

[phphe]

Hello

I have a Vue tree component that has been published for many years and is used by many people. Recently, I developed a React tree component just like it. Please check and leave comments.

The three libraries that already exist in the tree directory are awesome. Compared to them, he-tree-react has the following differences:

• A customizable placeholder for dropping.
• Both flat data and tree data are supported.
• No heavy inner methods for handling tree's data. I recommend using immer to update data. There are mutiple demo in docs about that.