[docs] Add links to the Tutorial

[t-kikuc]

What this PR does / why we need it:

I added links to the tutorial in

• README.md
• quickstart/_index.md

so that users can easily find the tutorial.

Which issue(s) this PR fixes:

N/A

Does this PR introduce a user-facing change?: N/A

• How are users affected by this change: N/A
• Is this breaking change: N/A
• How to migrate (if breaking change): N/A

[khanhtc1202]

Thank you

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.39%. Comparing base (98b4fc2) to head (b4ecdf9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4964   +/-   ##
=======================================
  Coverage   29.39%   29.39%           
=======================================
  Files         322      322           
  Lines       40852    40852           
=======================================
+ Hits        12007    12010    +3     
+ Misses      27885    27882    -3     
  Partials      960      960           

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[Warashi]

thank you