Adding PNF requirements in section 5.1.5

The requirement to support to PNF onboarding on Dublin release, need to add PNF related requriement.

Proposed change

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5.1.5. Overview

The document includes three charters to help the VNF/PNF providers to use the VNF/PNF model design tools and understand the VNF/PNF package structure and VNF/PNF TOSCA templates.

In the ONAP, VNF/PNF Package and VNFD/PNFD template can be designed manually or via model designer tools. VNF/PNF model designer tools can provide the GUI and CLI tools for the VNF/PNF provider to develop the VNF/PNF Package and VNFD/PNFD template.

The VNF/PNF package structure is based on the most updated ETSI GS NFV-SOL004 standard draft and leverages the TOSCA/YAML CSAR.

The VNFD/PNFD and VNF/PNF package are all aligned with TOSCA/YAML sepc which supports multiple TOSCA template yaml files, and also supports self-defined node or other extensions.

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