Add credits file

lib/settings/release.dart

@@ -24,4 +24,25 @@ class ReleaseNotesWidget extends StatelessWidget {
       )
     );
   }
+}
+
+
+class CreditsWidget extends StatelessWidget {
+
+  final String credits;
+
+  CreditsWidget(this.credits);
+
+  @override
+  Widget build (BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(I18N.of(context).credits),
+      ),
+      body: Markdown(
+        selectable: false,
+        data: credits
+      )
+    );
+  }
 }