doc: added an example HTML for umd. also fixed README of umd usage

[JinIgarashi]

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Description

closes #11

Type of Pull Request

• [ ] Adding a feature
• [ ] Fixing a bug
• [x] Maintaining documents
• [ ] Others ()

Verify the followings

• [x] Code is up-to-date with the main branch
• [x] No lint errors after pnpm lint
• [x] Make sure all the exsiting features working well

Refer to CONTRIBUTING.MD for more details.

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