404 in Bearer link in `linebot/v3/liff/docs/Liff.md`

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## Documentation

The link to [`Bearer`](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/README.md#Bearer) in the **add_liff_app, delete_liff_app, get_all_liff_apps, update_liff_app** section of [`linebot/v3/liff/docs/Liff.md`](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md) is broken and currently returns a 404 because there is no `README.md` in `linebot/v3/liff/docs`.

## Location

- File: `linebot/v3/liff/docs/Liff.md`
- Section: **add_liff_app, delete_liff_app, get_all_liff_apps, update_liff_app**
- Broken Link: [`Bearer`](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/README.md#Bearer)

## Steps to Reproduce

1. Navigate to [`linebot/v3/liff/docs/Liff.md`](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md).
2. Find the [**add_liff_app**](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md#add_liff_app), [**delete_liff_app**](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md#delete_liff_app), [**get_all_liff_apps**](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md#get_all_liff_apps), and [**update_liff_app**](https://github.com/line/line-bot-sdk-python/blob/master/linebot/v3/liff/docs/Liff.md#update_liff_app) section.
3. Click on the `Bearer` link.
4. Observe that it leads to a 404 error.

## Expected Behavior

The `Bearer` link should correctly navigate to the relevant section in the README file.

## Proposed Fix

Verify the correct anchor in `Bearer` and update the link to ensure it directs to the intended content.