Issue title: 没有 markdown 格式导出
 Issue body: ### What happened?

期望导出 markdown 格式文件

### Reproduce the Bug

导出弹窗没有 markdown 格式

### Expected Behavior

_No response_

### Screenshots

<img width="752" alt="image" src="https://user-images.githubusercontent.com/16385443/179143997-487c041e-5fff-428b-b791-9947bfcb48af.png">


### Desktop Platform Information

_No response_

### Mobile Platform Information

_No response_

### Additional Context

_No response_
 Comments: 
 Comment 0: Can you attach an English version? Thank you:)

The files are naturally stored in markdown by default (except you are using org-mode style editing), so you can use the `.md` files in the graph folder directory.
The `Text` option in the export panel is for exporting markdown in customized style.
 Comment 1: > Can you attach an English version? Thank you:)
> 
> The files are naturally stored in markdown by default (except you are using org-mode style editing), so you can use the `.md` files in the graph folder directory. The `Text` option in the export panel is for exporting markdown in customized style.

I see, thx
 Comment 2: > > Can you attach an English version? Thank you:)
> > The files are naturally stored in markdown by default (except you are using org-mode style editing), so you can use the `.md` files in the graph folder directory. The `Text` option in the export panel is for exporting markdown in customized style.
> 
> I see, thx Maybe this unordered list confuses me Could the unordered list be removed default?

Tuning the `indent style` option might help
<img width="439" alt="image" src="https://user-images.githubusercontent.com/9862022/179343737-0d9c761c-e27a-4d50-adec-5ad9ea42f476.png">
<img width="400" alt="image" src="https://user-images.githubusercontent.com/9862022/179343748-8958badd-8b09-411a-987f-c20a76a6beb2.png">

 Comment 3: > > > Can you attach an English version? Thank you:)
> > > The files are naturally stored in markdown by default (except you are using org-mode style editing), so you can use the `.md` files in the graph folder directory. The `Text` option in the export panel is for exporting markdown in customized style.
> > 
> > 
> > I see, thx Maybe this unordered list confuses me Could the unordered list be removed default?
> 
> Tuning the `Indentation style` option might help <img alt="image" width="400" src="https://user-images.githubusercontent.com/9862022/179343748-8958badd-8b09-411a-987f-c20a76a6beb2.png">

Thanks
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