Document platform key (#169)

Author: jonathanKingston

README.md

@@ -12,6 +12,8 @@ The exposed API is a global called contentScopeFeatures and has three methods:
 - init
     - Calls the init method on all of the features
     - This should be passed the arguments object which has the following keys:
+        - 'platform' which is an object with:
+            - 'name' which is a string of 'android', 'ios', 'macos' or 'extension'
         - 'debug' true if debuging should be enabled
         - 'globalPrivacyControlValue' false if the user has disabled GPC.
         - 'sessionKey' a unique session based key.
@@ -47,12 +49,22 @@ There are three stages that the content scope code is hooked into the platform:
 The [inject/](https://github.com/duckduckgo/content-scope-scripts/tree/main/inject) directory handles platform specific differences and is glue code into calling the contentScopeFeatures API.
 
 - In Firefox the code is loaded as a standard extension content script.
-- For Apple the code is a UserScript that has some string replacements for properties and loads in as the page scope.
+- For Apple, Windows and Android the code is a UserScript that has some string replacements for properties and loads in as the page scope.
     - Note: currently we don't implement the update calls as it's only required by cookie protections which we don't implement.
 - All other browsers the code is stringified, base64 encoded and injected in as a self deleting <script> tag.
 
 In the built output you will see these dramatic differences in the bundled code which is created into: /build
 
+#### App specific integration replacements
+
+$CONTENT_SCOPE$ - raw remote config object
+$USER_UNPROTECTED_DOMAINS$ - an array of user allowlisted domains
+$USER_PREFERENCES$ - an object containing:
+    platform: { name: '<ios | macos | extension | android>' }
+    debug: boolean
+    globalPrivacyControlValue: boolean
+    sessionKey: <random UUID string> (used for fingerprinting)
+
 ### Features scope injection utilities
 
 To handle the difference in scope injection we expose multiple utilities which behave differently per browser in src/utils.js. for Firefox the code exposed handles [xrays correctly](https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts) without needing the features to be authored differently.