documentation(boards): add documentation for native_sim

[SorinOlari]

Description

added documentation for native_sim board

• Related to issue # Documentation #138

Type of change

• This change requires a 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
• New and existing unit tests pass locally with my changes

[casaroli]

Isn't it supported?

[kr-t]

if you check https://github.com/project-ocre/ocre-runtime/tree/main/src/samples/demo/zephyr/boards or https://github.com/project-ocre/ocre-runtime/tree/main/src/samples/supervisor/zephyr/boards, we only have native_sim_64.conf/overlay. For the 32b version we probably need to copy 64b configs, rename them and test them. I don't expect them to be different a lot if at all.