fix: add dev script to enter dev mode in root, and change readme.

[ederzz]

Types of changes

• [ ] New feature
• [x] Bug fix
• [ ] Documentation change
• [ ] Coding style change
• [ ] Refactoring
• [ ] Performance improvement
• [ ] Test cases
• [ ] Continuous integration
• [ ] Typescript definition change
• [ ] Breaking change

Background and context

The script enter dev mode in readme is not work.

Solution

Add a new script: dev in root package, exec lerna run dev with --parallel.

How is the change tested?

Changelog

Changelog(CN)	Changelog(EN)	Related issues

Checklist:

• [ ] Provide changelog for relevant changes (e.g. bug fixes and new features) if applicable.
• [ ] Changes are submitted to the appropriate branch (e.g. features should be submitted to feature branch and others should be submitted to master branch)

Other information

[ederzz]

@MisterLuffy cc