Add TUTORIAL and FAQ in Sedna's Documentation

[Lj1ang]

What would you like to be documented:

• TUTORIAL: instructs users to customize their own cases.
• FAQ: records frequently asked questions and corresponding solutions.

Why is this needed:
At present, Sedna's documentation doesn't teach users how to use Sedna very well. INTRODUCTION part tells about how Sedna's features are developed and EXAMPLE part is about how to quickly run the examples provided in Sedna. Neither of the two parts instructs users to customize their own cases based on Sedna's API.

[MooreZheng]

As mentioned, EXAMPLE part is about how to quickly run the examples provided in Sedna. It is important to have documents for further developing examples. /assign @luosiqi might help to follow up the issue.

[Lj1ang]

/assign @luosiqi

[kubeedge-bot]

@Lj1ang: GitHub didn't allow me to assign the following users: luosiqi.

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In response to this:

/assign @luosiqi

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[MooreZheng]

hi @luosiqi pls also follow up this issue

[MooreZheng]

We have wonderful contributors working on these issues.
@luosiqi #391 Proposal and tutorial of unstructured lifelong learning
@qxygxt #401 Tutorial for ATCII Lifelong Learning Job