doc: imporove "Getting Started" section

[Jannchie]

Clear and concise description of the problem

Hello everyone. I am learning to use vitest. This library seems to assume that all users have experience with jest. Even though I have previous experience with jest development, I am still a bit confused.

As a new user to vitest, I think it is essential to provide examples of how to use the basic api in the "Getting Started" section. However, I see a lot of exciting ways to use vite's advanced features, but I can't find out exactly how I'm supposed to create a unit test.

Suggested solution

I think we can simply refer to jest (https://jestjs.io/docs/getting-started) and add examples of usage.

Although I'm not a native English speaker. I am willing to write a draft if you maintainers find this issue valuable.

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.