[doco/RFA] Fix subject verb agreement in the description of several debug settings.

[Eli Zaretskii]

> Date: Tue, 26 Jan 2016 16:38:09 +0400
> From: Joel Brobecker <brobecker@adacore.com>
> Cc: gdb-patches@sourceware.org, eliz@gnu.org
> 
> Adding [doco] to the subject, to alert Eli, our doc reviewer...
> 
> On Fri, Jan 22, 2016 at 09:03:48AM -0800, John Baldwin wrote:
> > gdb/doc/ChangeLog:
> > 
> > 	* gdb.texinfo (Debugging Output): Fix subject verb disagreements.

Fine with me, thanks.

(I did think it was being committed as obvious.)