Adds other StackExchange site support

[Zo-Bro-23]

• [x] New parameter site={SITE}
• [x] New error message
• [x] Updated documentation for the new parameter
• [x] Updated vercel.json to comply with new Vercel schema (@now/node-server is not valid anymore)
• [ ] Custom site icons for badges (will probably have to use SE sprites for this)

[vercel[bot]]

Someone is attempting to deploy a commit to a Personal Account owned by @omidnikrah on Vercel.

@omidnikrah first needs to authorize it.