view_pdf_file example added (#57)

* view_pdf_file example added

* made revelent changes

changed package, example of both load pdf from asset and url, added link from example in readme

* added example view_pdf_file

* Added View PDF File example

* minor changes

view_pdf_file/lib/viewPDF.dart

@@ -0,0 +1,19 @@
+import 'package:advance_pdf_viewer/advance_pdf_viewer.dart';
+import 'package:flutter/material.dart';
+
+class ViewPDF extends StatelessWidget {
+  final PDFDocument doc;
+  ViewPDF({
+    @required this.doc,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('Example'),
+      ),
+      body: Center(child: PDFViewer(document: doc)),
+    );
+  }
+}