Addon-docs mdx docs disappeared on the menu when using --docs

Describe the bug When I start a project by add --docs, it seems disappeared in left menu I can access this page by typing the url, but can not find it on the left.

Actually, I can see it if I don’t start a docs-only page.

To Reproduce NODE_PATH=src start-storybook -c .storybook -p 6006 --docs

Expected behavior Show items when use --docs

Code snippets mdxfile

import { Meta, Story, Props, Preview } from '@storybook/addon-docs/blocks';
import { text, object } from '@storybook/addon-knobs';
import getConfig from '../utils/getConfig';

<Meta title="Xtable" component={Live} />

## 代码演示
....
<Preview withToolbar mdxSource={BasicText}>
  <Story name="基本例子">
    <Basic />
  </Story>
</Preview>

## Live Demo
 ...
<Story name="live-demo" args={config}>
  {(args) => {
    return <Live {...args} />
  }}
</Story>

<Props story="live-demo" />

System: System: OS: macOS Mojave 10.14.5 CPU: (8) x64 Intel® Core™ i7-4771 CPU @ 3.50GHz Binaries: Node: 12.16.1 - /usr/local/bin/node Yarn: 1.22.4 - /usr/local/bin/yarn npm: 6.13.4 - /usr/local/bin/npm Browsers: Chrome: 81.0.4044.122 Safari: 12.1.1 npmPackages: @storybook/addon-docs: ^6.0.0-alpha.39 => 6.0.0-alpha.41 @storybook/addon-knobs: ^6.0.0-alpha.41 => 6.0.0-alpha.41 @storybook/react: ^6.0.0-alpha.41 => 6.0.0-alpha.41 @storybook/source-loader: ^6.0.0-alpha.41 => 6.0.0-alpha.41

Additional context Add any other context about the problem here.

[domyen]

So the request seems to be seeing stories as nested elements in the sidebar of the --docs page?

That’s not the common behavior in most design systems I researched, however I could see why folks might want to quickly navigate to the story section.

I don’t think it makes sense to link to every story but perhaps we can auto-generate nested sidebar elements for all h2s instead. That’s inline with typical documentation site behavior and is general enough to apply to many cases. (We also dogfood --docs mode for Storybook Design System)

[shilman]

That’s a feature of --docs, not a bug