[docs] Add missing events to docs/events page (#2123)

* [docs] Add missing evens to docs/events page

Added missing `onReset` event to Form Events –– (https://reactjs.org/docs/events.html#form-events)
Created Generic Events subsection, and added `onError` & `onLoad` events –– (https://reactjs.org/docs/events.html#generic-events)

Based on @sophiebits suggestion in following thread:
https://github.com/facebook/react/issues/1718#issuecomment-122622933

* [docs] Add event subsection to #supported-events

Added Generic Events subsection under Supported Events (https://reactjs.org/docs/events.html#supported-events)

content/docs/reference-events.md

@@ -76,6 +76,7 @@ The event handlers below are triggered by an event in the bubbling phase. To reg
 - [Keyboard Events](#keyboard-events)
 - [Focus Events](#focus-events)
 - [Form Events](#form-events)
+- [Generic Events](#generic-events)
 - [Mouse Events](#mouse-events)
 - [Pointer Events](#pointer-events)
 - [Selection Events](#selection-events)
@@ -177,13 +178,23 @@ DOMEventTarget relatedTarget
 Event names:
 
 ```
-onChange onInput onInvalid onSubmit
+onChange onInput onInvalid onReset onSubmit 
 ```
 
 For more information about the onChange event, see [Forms](/docs/forms.html).
 
 * * *
 
+### Generic Events {#generic-events}
+
+Event names:
+
+```
+onError onLoad
+```
+
+* * *
+
 ### Mouse Events {#mouse-events}
 
 Event names: