Improve docs on theming

Author: carbonrobot

README.md

@@ -39,8 +39,6 @@ _(If you just want to use your Prism CSS-file themes, that's also no problem)_
 ## Table of Contents
 
 <!-- START doctoc generated TOC please keep comment here to allow auto update -->
-<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
-
 
 - [Installation](#installation)
   - [Usage](#usage)
@@ -58,11 +56,18 @@ _(If you just want to use your Prism CSS-file themes, that's also no problem)_
     - [`getLineProps`](#getlineprops)
     - [`getTokenProps`](#gettokenprops)
 - [Utility Functions](#utility-functions)
-  - [`normalizeTokens`](#normalizetokens)
   - [`useTokenize`](#usetokenize)
+  - [`normalizeTokens`](#normalizetokens)
 - [Theming](#theming)
-- [Upgrading from v1 to v2](#upgrade)
-- [Local Development](#development)
+  - [Using a built-in theme](#using-a-built-in-theme)
+  - [Providing a CSS based theme](#providing-a-css-based-theme)
+- [Upgrade](#upgrade)
+  - [Change module imports](#change-module-imports)
+  - [Change theme imports](#change-theme-imports)
+  - [Check language support](#check-language-support)
+  - [Add language component](#add-language-component)
+- [Development](#development)
+  - [Local Demo](#local-demo)
 - [LICENSE](#license)
 - [Maintenance Status](#maintenance-status)
 
@@ -85,7 +90,8 @@ pnpm add prism-react-renderer
 > Prism React Renderer has a peer dependency on `react`
 
 ### Usage
-Prism React Renderer has a named export for the `<Highlight />` component along with `themes`. To see Prism React Render in action with base styling check out `packages/demo` or run `pnpm run start:demo` from the root of this repository.
+
+Prism React Renderer has a named export for the `<Highlight />` component along with `themes`. To see Prism React Render in action with base styling, clone the repo and follow the [steps for local development](#development).
 
 ```tsx
 import React from "react"
@@ -133,7 +139,7 @@ ReactDOM
 
 ### Custom Language Support
 
-By default `prism-react-renderer` only includes a [base set of languages](https://github.com/FormidableLabs/prism-react-renderer/blob/c914fdea48625ba59c8022174bb3df1ed802ce4d/packages/generate-prism-languages/index.ts#L9-L23) that Prism supports. 
+By default `prism-react-renderer` only includes a [base set of languages](https://github.com/FormidableLabs/prism-react-renderer/blob/master/packages/generate-prism-languages/index.ts#L9-L23) that Prism supports. 
 
 > _Note_: Some languages (such as Javascript) are part of the bundle of other languages
 
@@ -328,12 +334,11 @@ Takes an array of Prism’s tokens and groups them by line, converting strings i
 
 ## Theming
 
+### Using a built-in theme
+
 The `defaultProps` you'd typically apply in a basic use-case, contain a default theme.
 This theme is [vsDark](./packages/prism-react-renderer/src/themes/vsDark.ts).
 
-While all `className`s are provided with `<Highlight />`, so that you could use your good
-old Prism CSS-file themes, you can also choose to use `prism-react-renderer`'s themes like so:
-
 ```jsx
 import { Highlight, themes } from 'prism-react-renderer';
 
@@ -367,6 +372,16 @@ property limits styles to highlighted languages.
 When converting a Prism CSS theme it's mostly just necessary to use classes as
 `types` and convert the declarations to object-style-syntax and put them on `style`.
 
+### Providing a CSS based theme
+
+In order to use a CSS based theme like the ones from [PrismJS](https://github.com/PrismJS/prism-themes), you need to disable the built in theme.
+
+```ts
+const emptyTheme = { plain: {}, styles: [] };
+
+<Highlight theme={emptyTheme} {/* ... */} />
+```
+
 ## Upgrade
 
 If you are migrating from v1.x to v2.x, follow these steps