Document implemented APIs at the top

lib/renderer/window-setup.js

@@ -2,6 +2,25 @@
 // preload bundle. Instead arguments should be passed in for everything it
 // needs.
 
+// This file implements the following APIs:
+// - window.alert()
+// - window.confirm()
+// - window.history.back()
+// - window.history.forward()
+// - window.history.go()
+// - window.history.length
+// - window.open()
+// - window.opener.blur()
+// - window.opener.close()
+// - window.opener.eval()
+// - window.opener.focus()
+// - window.opener.location
+// - window.opener.print()
+// - window.opener.postMessage()
+// - window.prompt()
+// - document.hidden
+// - document.visibilityState
+
 'use strict'
 
 const {defineProperty} = Object