EDITING: (GET-STARTED) Simplify and actualize `GetStarted` section

[azinit]

Problem

• The current tutorial can not be called a “quick start", because it contains a lot of details
  (for seniors - redundant, for juniors - not enough)
• Also, he is too tied to React, which knocks other people down
• In addition, the tutorial does not teach the application of the basics of the "slicing UI" methodology well

Subtasks

• EDITING: (GET-STARTED) Remove redundant impl-specific content #454
• EDITING: (GET-STARTED) Add visual framework-agnostic tutorial #455
• If need, add more tutorials... (impl-speficic, quick-migration, ...)