Move to Fly.io

[LitoMore]

We're planning to move this service from Vercel to Fly.io.

The code is ready on the https://github.com/LitoMore/simple-icons-cdn/tree/main branch.

Todo

• Setup Fly.io app (https://simple-icon-cdn.fly.dev) (@LitoMore)
• Move domain icons.ly from Vercel to Fly.io (@LitoMore)
• Update domain cdn.simpleicons.org DNS (@mondeja)
• Move domain cdn.simpleicons.org from Vercel to Fly.io (@LitoMore)
• Add Fly.io icon to Simple Icons (Add Fly.io icon simple-icons/simple-icons#11025) (@LitoMore)