Add documentation and changelog

Author: bbrala

CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Changelog ##
 
+### Unreleased
+
+#### Added
+
+* Added support for `events.preShow` so you can enable default browser menu if needed (thanks @terwarf)
+
 ### 2.7.1
 
 #### Fixed

documentation/docs.md

@@ -307,7 +307,8 @@ A reference to the current options object is passed, the options object is a col
 
 Value | Description
 ---- | ---- 
-`events.show` | Called before show of the contextmenu 
+`events.preShow` | Called before show of the contextmenu, when returning false default browser context menu is shown
+`events.show` | Called on show of the contextmenu 
 `events.hide` | Called before hide of the contextmenu
 `events.activated` | Called after activation of the contextmenu