HomeScreen: Show some text when we have no journal entries

Ideally, I would want something way prettier, but this is a good
enough start.

lib/screens/home_screen.dart

@@ -20,7 +20,9 @@ class HomeScreen extends StatelessWidget {
       child: Icon(Icons.add),
     );
 
-    var journalList = JournalList(
+    Widget journalList;
+    if (appState.notes.isNotEmpty) {
+      journalList = JournalList(
         notes: appState.notes,
         noteSelectedFunction: (noteIndex) {
           var route = MaterialPageRoute(
@@ -32,6 +34,19 @@ class HomeScreen extends StatelessWidget {
           Navigator.of(context).push(route);
         },
       );
+    } else {
+      journalList = Center(
+        child: Text(
+          "Why not add your first\n Journal Entry?",
+          textAlign: TextAlign.center,
+          style: TextStyle(
+            fontSize: 28.0,
+            fontWeight: FontWeight.w300,
+            color: Colors.grey[350],
+          ),
+        ),
+      );
+    }
 
     bool shouldShowBadge =
         !appState.remoteGitRepoConfigured && appState.hasJournalEntries;