Add docs about deeplinking to README

README.md

@@ -40,6 +40,18 @@ We're following a set of principles inspired by protobuf versioning:
 - don't modify existing API call signatures
 - adding new APIs in the Electron app is ok, in the web client these should be optionally typed, and checked for existence dynamically (`if ('logout2' in replitDesktop) { ... }`)
 
+## Deeplinking
+
+The app supports deeplinks with the `replit://` protocol which can be used to open specific pages or flows directly, launching the app if it's not already running.
+
+The following deeplinks are currently supported:
+- `replit://home`: Opens the desktop app home page in the focused window (or a new window if none are open).
+- `replit://new`: Opens a new window which launches the Repl creation flow.
+  - Optionally accepts a `language` string param which prefills the new Repl modal with that language's template (defaults to Python).
+- `replit://authComplete`: Completes the authentication flow which is triggered by the app during the login process, which redirects to the browser to generate a valid auth token that can be exchanged in order to authenticate the user associated with the browser's session. No-op if the user is already logged in.
+  - Requires an `authToken` string param which represents a valid auth token generated by the repl-it-web server that is necessary to complete the authentication process.
+- `replit://repl/@:username/:slug`: Opens the Repl associated with that username and slug in the focused window (or a new one if none are open).
+
 ## Release
 
 To publish a new release of the app, run the release script like so: