[Packages] Add docs for the state populated by the Frontity core package

[DAreRodz]

In the same fashion other packages do (e.g. @frontity/wp-source), the frontity package also exposes state that other packages may use.

The state properties and their description can be found in this file of the frontity monorepo: /packages/types/src/frontity.ts

[juanmaguitar]

@DAreRodz

When you say

the frontity package also exposes state that other packages may use.

Do you mean @frontity/core package, right?

And, are you referring specifically to document these properties that can be seen under state.frontity?

"{
  "url": "https://twentytwenty.frontity.org",
  "title": "Test Frontity Blog",
  "description": "Useful content for Frontity development",
  "name": "twentytwenty-theme",
  "mode": "default",
  "debug": false,
  "platform": "client",
  "rendering": "csr",
  "initialLink": "/",
  "options": {},
  "packages": [
    "@frontity/tiny-router",
    "@frontity/html2react",
    "@frontity/twentytwenty-theme",
    "@frontity/wp-source"
  ]
}"