bug#24511: 24.5; Timer docs don't mention timerp

[Eli Zaretskii]

> From: endian@gmail.com
> Date: Thu, 22 Sep 2016 17:01:28 +0000
> 
> 
> The timer docs at
> 
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Timers.html
> 
> contain no mention of the timerp function and it should.

Thanks, added.