Add missing required sections to the UI and CLI documentation

[maelvls]

The Google documentation states that the user guide should contain certain sections. In the following list, I have checked the items that we already have:

• Overview
• One-time setup
• Installation
• Basic Usage (I added a section where I explain how to create a certificate)
• Back up and restore
• Image updates
• Scaling
• Deletion

This issue aims at reminding us to add the 4 missing sections both for the UI and the CLI instructions.