Fix podspec for Swift

+# 1.3.4
+* Fix iOS build with Swift
+* Add installation instructions in the Readme
+
 # 1.3.3
 # 1.3.3
 * Fix dart lint warnings
 * Fix dart lint warnings
 * Add documentation
 * Add documentation

@@ -34,3 +34,29 @@ PdfTtfFont ttf = PdfTtfFont(pdf, font);
 g.setColor(PdfColor(0.3, 0.3, 0.3));
 g.setColor(PdfColor(0.3, 0.3, 0.3));
 g.drawString(ttf, 20.0, "Dart is awesome", 50.0, 30.0);
 g.drawString(ttf, 20.0, "Dart is awesome", 50.0, 30.0);
 ```
 ```
+
+## Installing
+
+1. Add this to your package's `pubspec.yaml` file:
+
+   ```yaml
+   dependencies:
+     printing: any       # <-- Add this line
+   ```
+
+2. Enable Swift on the iOS project, in `ios/Podfile`:
+
+   ```Ruby
+   target 'Runner' do
+      use_frameworks!    # <-- Add this line
+   ```
+
+3. Set minimum Android version in `android/app/build.gradle`:
+
+   ```java
+   defaultConfig {
+       ...
+       minSdkVersion 19  // <-- Change this line to 19 or more
+       ...
+   }
+   ```

 # Pdf Printing Example
 # Pdf Printing Example
 
 
 ```dart
 ```dart
-void printPdf() {
-  Printing.layoutPdf(onLayout: (PdfPageFormat format) {
-    final pdf = Document()
-      ..addPage(Page(
-          pageFormat: PdfPageFormat.a4,
-          build: (Context context) {
-            return Center(
-              child: Text("Hello World"),
-            ); // Center
+import 'dart:async';
+import 'package:flutter/material.dart';
+
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart' as Pdf;
+import 'package:printing/printing.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        appBar: AppBar(
+          title: Text('Printing Demo'),
+        ),
+        body: Center(
+          child: FlatButton(
+            child: Text("Print Document"),
+            onPressed: () {
+              Printing.layoutPdf(onLayout: buildPdf);
+            },
+          ),
+        ),
+      ),
+    );
+  }
+
+  List<int> buildPdf(PdfPageFormat format) {
+    final PdfDoc pdf = PdfDoc()
+      ..addPage(Pdf.Page(
+          pageFormat: format,
+          build: (Pdf.Context context) {
+            return Pdf.ConstrainedBox(
+              constraints: const Pdf.BoxConstraints.expand(),
+              child: Pdf.FittedBox(
+                  child: Pdf.Text(
+                "Hello World",
+              )),
+            );
           }));
           }));
-    return pdf.save();
-  }); // Page
+    return pdf.document.save();
+  }
 }
 }
 ```
 ```

@@ -17,5 +17,5 @@ Plugin that allows Flutter apps to generate and print documents to android or io
   s.dependency 'Flutter'
   s.dependency 'Flutter'
   
   
   s.ios.deployment_target = '8.0'
   s.ios.deployment_target = '8.0'
+  s.swift_version = '4.2'
 end
 end
-

@@ -2,7 +2,7 @@ name: printing
 author: David PHAM-VAN <dev.nfet.net@gmail.com>
 author: David PHAM-VAN <dev.nfet.net@gmail.com>
 description: Plugin that allows Flutter apps to generate and print documents to android or ios compatible printers
 description: Plugin that allows Flutter apps to generate and print documents to android or ios compatible printers
 homepage: https://github.com/DavBfr/dart_pdf/tree/master/printing
 homepage: https://github.com/DavBfr/dart_pdf/tree/master/printing
-version: 1.3.3
+version: 1.3.4
 
 
 environment:
 environment:
   sdk: ">=1.19.0 <3.0.0"
   sdk: ">=1.19.0 <3.0.0"