Advise users to flash stock ROM before applying an upgrade

Summary

In upgrade documentation, we should highlight that users might have to flash the last stock ROM available for their device before installing the last update.

Description

What is the current behavior?

We have a warning on the topic

What is the improved behavior?

This warning should become a specific step in the upgrade process

What does it bring?

We are sure user will not skip this step.

Examples

Validation