Need to describe the process for a customer to implement the N+ version

[brianehlert]

trafficstars

There is a doc that covers pulling the N+ image, however there is no clear explanation for supported customers at how they would go through the process of moving from the free implementation to the paid implementation (replacing NGINX OSS with NGINX Plus).

• how to deploy NGF with N+
• how to move from free to paid (deploy new, in-place upgrade)
• what the customers can expect if they in-place upgrade an existing deployment