[Feature] Add Synology NAS documentation

[acud]

I have searched the existing feature requests to make sure this is not a duplicate request.

• Yes

The feature

I've been running Immich on a Synology NAS (including the QSV hardware transcoding) and thought it might be nice to contribute to the docs section as there's no user-facing documentation on how to set this up easily on Synology, and information must be pieced from different sources in order to get it to work.

If this sounds reasonable, I'm happy to contribute to this effort with a PR.

Platform

• Server
• Web
• Mobile