added comment for fn step class

Author: DavertMik

lib/step/func.js

@@ -5,17 +5,21 @@ const store = require('../store')
  * Function executed as a step
  */
 class FuncStep extends BaseStep {
+  // this is actual function that should be executed within step
   setCallable(fn) {
     this.fn = fn
   }
 
+  // helper is optional, if we need to allow step to access helper methods
   setHelper(helper) {
     this.helper = helper
   }
 
   run() {
     if (!this.fn) throw new Error('Function is not set')
 
+    // we wrap that function to track time and status
+    // and disable it in dry run mode
     this.args = Array.prototype.slice.call(arguments)
     this.startTime = +Date.now()