Explain nickname property in version object (#46)

Author: Paul Verbeek-Mast

README.md

@@ -494,6 +494,8 @@ An object of the `Version` class is used for the `version` property of the `Brow
   a string containing the original version number.
 * `alias`  
   a string containing an alias for the version number, ie. 'XP' for Windows '5.1'.
+* `nickname`  
+  a string containing a nickname for the version number, ie. 'Mojave' for OS X '10.14'.
 * `details`  
   an integer containing the number of digits of the version number that should be printed.