Add info about event editing [ci skip]

README.md

 `2` indicates a malformed request.
 
 ### /events/edit/:eventid
-To create a new event, a `PUT` request should be sent with the following data:
+To create a new event, a `PUT` request should be sent with the following data -
+all fields except auth are optional:
 ```javascript
 {
     "name": "Test Event",