Outdated image: documentation and warning

[peterpeterparker]

Motivation

Starting the cli or the emulator should check weekly the version, particularly for the emulator as mentionned by @AntonioVentilii, it's not clear how and when to update the emulator.

In addition to automatic checks, we should also document how on the website.

[peterpeterparker]

The automatic checks has been shipped in the Juno CLI https://github.com/junobuild/cli/releases/tag/v0.14.2

Keeping the tast open for the documentation part