🚀 Feature

Currently, EventEnum is absent in the docs and below there is no link in the docs:

https://pytorch.org/ignite/master/engine.html#ignite.engine.events.Events

Idea is to introduce it in the docs by adding a docstring here

and improve above and all other examples where EventEnum is mentioned (please, search for it in the whole repository) by adding

from ignite.engine import EventEnum

For Hacktoberfest contributors, feel free to ask questions for details if any and say that you would like to tackle the issue.
Please, take a look at CONTRIBUTING guide.