Events doc fixes

Documentation fix for #8853 ... specifically, acknowledge in the docs that EE.addListener(...) does not check to see if the given listener has already been added, and that newListener will be called regardless of whether an already existing listener is added twice.
>'Then you should say what you mean,' the March Hare went on."  - https://www.cs.cmu.edu/~rgs/alice-VII.html

If that's what it was trying to say it was rather a poor attempt at it indeed.