Remove Swift Version from plugin.xml and document config.xml preference

Closes #342
Closes #335
Closes #382

Author: NiklasMerz

README.md

@@ -31,6 +31,7 @@ _Version 4 was developed almost 100% by other people than me (@NiklasMerz)._ **P
 
 * Android - Minimum SDK 23
 * iOS - **latest XCode** is required. Plugin sets Swift version 4.
+  * _Please set `<preference name="SwiftVersion" value="5.0" />` in your config.xml_
 * Mac via Catalyst. If you run the iOS platform on a Mac the plugin will ask for the user password and work with like on other platforms.
 * The [cordova-osx](https://github.com/apache/cordova-osx) platform is not supported
 

plugin.xml

@@ -17,7 +17,6 @@
     <header-file src="src/ios/Bridging-Header.h" type="BridgingHeader"/>
     <source-file src="src/ios/Fingerprint.swift"/>
     <config-file target="config.xml" parent="/*">
-      <preference name="SwiftVersion" value="4"/>
       <feature name="Fingerprint">
         <param name="ios-package" value="Fingerprint"/>
       </feature>