docs: update README for auth dialogs

Author: heyzec

README.md

@@ -45,7 +45,12 @@ After installing the extension,
 
 Alternatively, use the `Source Academy: Show the Source Academy Panel` command.
 
-Once the panel loads, you'll be prompted to log in. Afterwards, begin coding by opening any assessment.
+3. Choose a login method and authenticate in your browser.
+
+- When prompted, click **Open** to proceed to the external website.
+- After login, click **Open** again to allow the extension to open the URI. Optionally, check `Do not ask me again for this extension`.
+
+4. You may now begin coding by opening any assessment.
 
 ### Changing the frontend