Update README.md

Author: timsuchanek

README.md

@@ -248,6 +248,36 @@ $ yarn start
 Open
 [localhost:3000/localDev.html?endpoint=https://api.graph.cool/simple/v1/swapi](http://localhost:3000/localDev.html?endpoint=https://api.graph.cool/simple/v1/swapi) for local development!
 
+## Custom Theme
+From `[email protected]` on you can provide a `codeTheme` property to the React Component to customize your color theme.
+These are the available options:
+```ts
+
+export interface EditorColours {
+  property: string
+  comment: string
+  punctuation: string
+  keyword: string
+  def: string
+  qualifier: string
+  attribute: string
+  number: string
+  string: string
+  builtin: string
+  string2: string
+  variable: string
+  meta: string
+  atom: string
+  ws: string
+  selection: string
+  cursorColor: string
+  editorBackground: string
+  resultBackground: string
+  leftDrawerBackground: string
+  rightDrawerBackground: string
+}
+```
+
 ### Versions
 
 This is repository is a "mono repo" and contains multiple packages using [Yarn workspaces](https://yarnpkg.com/lang/en/docs/workspaces/). Please be aware that versions are **not** synchronised between packages. The versions of the [release page](https://github.com/graphcool/graphql-playground/releases) refer to the electron app.