update README & add .swift-version file

Diego Ernst · Diego Ernst · commit 6aa28e255d1a · 2017-09-27T11:31:33.000-03:00
diff --git a/.swift-version b/.swift-version
@@ -0,0 +1 @@
+4.0
diff --git a/README.md b/README.md
@@ -54,7 +54,7 @@ class ViewController: FormViewController {
 ## Requirements
 
 * iOS 8.0+
-* Xcode 8.3+
+* Xcode 9.0+
 
 ## Getting involved
 
