Edit new installation instructions

What does this Merge Request do?

Following up from !1495 (merged), make sure the new installation process if covered everywhere.

Closes: #1053 (closed).

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.