add content for section on how to prepare data package for submission to repository

[artinthetrees]

How data packaging interfaces with/eases repository submission (generally, and at least one specific example)

• already added a placeholder section on the website
• now, add content, including:
• general overview of how to create a shareable data package starting with a data package
• specific example 1: how to create and submit shareable data package(s) required for submission to Vivli clinical trials repository, and how to submit