Synology migration update

[petervanrijt]

Added:

• Instruction for data migration MongoDB Atlas to Synology.
• Useful Facebook links.
• Concept of the visual process of migration from Heroku and Atlas to a Synology.

[psonnera]

@petervanrijt Does it make sense to rewrite this document in nightscout.github.io or should it be left as a link? In terms of work to be done and updates I'm ok with the link solution.

[petervanrijt]

Thanks for stepping in. For now as a concept I think it's OK, but for preserving and editing information I see value in converting it. Probably will curse a few times when working on it ;)

[psonnera]

@petervanrijt looking at https://github.com/forgetyan/nightscout-synology I'm wondering if your work is complete or stale and what should be done with https://nightscout.github.io/vendors/synology/new_user/