[#6600] Docs: restructure the getting started docs

[tengqm]

Related: #6600

This PR restructures the getting-started tutorial. Changes include:

• push the getting started tutorial into a separate directory;
• remove duplicated instructions on install and configuration;
• rework the flow of information for clarity and conciseness.

[tengqm]

/assign @jerryshao

[jerryshao]

Thanks @tengqm for the work, I will review this PR soon.

[jerryshao]

@tengqm We use Github issue to track the works, so before submitting a PR, we should create a corresponding issue to describe what we should do, follow our PR title and description template to link to that issue, can you please do that?

[tengqm]

@tengqm We use Github issue to track the works, so before submitting a PR, we should create a corresponding issue to describe what we should do, follow our PR title and description template to link to that issue, can you please do that?

Good to know. Revised PR description, pointing to a newly filed EPIC issue.

[jerryshao]

Can you please keep the .md suffix, so the link can be worked in Github preview.

[tengqm]

Okay, will check it.

[jerryshao]

Does it work for the markdown syntax?

[tengqm]

Yes. It works. It is the official way of adding comments to Markdown.