Add info in `test/ui-test` README.md to unify criterias

[noeliaSD]

Description

• Squish IDE project config

• Coding convention

  • naming conventions
  • python used notation (snake case)

• Implementation

  • abstraction layer parts where to use squish imports
  • habits

[MishkaRogachev]

Suggestions:

• Tab policy - only spaces. Clean whitespaces & indentation
• Rules how to name object names of QML components and aliases in ***_names.py
• Rules for error throwing & debug output in squish tests

[noeliaSD]

• IDE proper configuration
• Project structure (shared stuff, test cases and suites structure)