Documentation about Outgoing Connections

[coolwanglu]

firewall.md lists a few hosts that should be allowed by firewall. I think we should further specify "which firewall".

Here's my findings, not necessarily accurate:

• Server Setup
  • dl.photoprism.app
• Running Server
  • my.photoprism.app
  • places.photoprism.app
• Client (e.g. browser)
  • cdn.photoprism.app
  • maps.photoprism.app
• Not Used (removed?)
  • places.photoprism.xyz