Write paragraph 4.2 Major design issues

[illia-kriukov]

Describe major design issues:

• Important issues that had to be resolved;
• All alternatives you considered, the final decision and the rationale for it.
  See details in the report document https://docs.google.com/document/d/1fRFAq2tTrNhpVkYdQO_XkQ6LCikQSEq2bGiZA2Kungc/edit