Document Subsets offered and unify naming

[Immortalin]

Font Name (Geist Sans/Geist Mono):

• Geist Sans
• Geist Mono

Description of the Issue:
When using Geist through next/fonts/google, there is the 'subset' parameter. Geist should document the specific subsets offered by this font beyond 'latin'. Geist through Google Fonts uses the Geist() constructor, while the vercel package uses GeistSans.

Steps to Reproduce:

const geist = Geist({
  subsets: ['latin'],
  display: 'swap',
})

const geistSans = GeistSans({
  subsets: ['latin'],
  display: 'swap',
})

Additional Context:
Geist/GeistSans should probably be unified.