fix: update the readme android settings (#47)

Author: simeng-li

README.md

@@ -103,7 +103,7 @@ Android
 In order to capture the callback url from Logto's sign-in web page, you will need to register your sign-in redirectUri to the `AndroidManifest.xml`.
 
 ```xml
-<activity android:name="com.linusu.flutter_web_auth.CallbackActivity" android:exported="false">
+<activity android:name="com.linusu.flutter_web_auth.CallbackActivity" android:exported="true">
     <intent-filter android:label="flutter_web_auth">
         <action android:name="android.intent.action.VIEW"/>
         <category android:name="android.intent.category.DEFAULT"/>