[yocto] doc nit

[Trevor Woerner]

Hi,

The Yocto Project Development Manual, section 3.2.2 (Source Control
Management (SCM)) states that:

"Git is a distributed system that is easy to
backup (each checkout is a backup in itself)"

I'm not 100% sure a "checkout" would be considered a backup. I think
most people would say that a "clone" is more like a backup than a
"checkout". No?

Best regards,
    Trevor