docs: update readme and docs

Author: funwithflutter

README.md

@@ -1,4 +1,4 @@
-<p align="center"><img src="assets/lit.png" height="125" alt="Lit Firebase"></p>
+<p align="center"><img src="https://raw.githubusercontent.com/funwithflutter/lit_firebase_auth/assets/lit.png" height="125" alt="Lit Firebase"></p>
 
 <h1 align="center" style="margin-top: 0px; font-size: 4em;">Lit Firebase Auth</h1>
 
@@ -140,6 +140,7 @@ LitAuth(
 ```
 
 This will use the default configuration and UI theming. See the section on decoration and theming for customization.
+**NOTE**: This widget needs to be below a `Scaffold` widget.
 
 ### Handle auth state changes
 To determine the current auth state, make use of `LitAuthState`:

lib/src/presentation/lit_auth_ui.dart

@@ -66,6 +66,9 @@ class LitAuthState extends StatelessWidget {
 typedef AuthFailureCallback = void Function(AuthFailure failure);
 
 /// The main widget to do any form of Authentication using **LitFirebaseAuth**.
+///
+/// Must be below a [Scaffold].
+///
 /// This widget is used to configure the UI, provide decorations/themes, or
 /// override the standard sign-in widget with a custom implementation.
 ///