documentation: Update getting started zephyr document

[SorinOlari]

Description

• specifying the zephyr version for west init
• added ocre clone step
• fixed path for west build

Type of change

Please delete options that are not relevant.

• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes