bug#35580: hexl-mode documentation is confusing about insertion

[Eli Zaretskii]

> From: Reuben Thomas <rrt@sc3d.org>
> Date: Sun, 5 May 2019 13:53:55 +0100
> 
>   Ordinary text characters overwrite in Hexl mode.  This is to reduce
> the risk of accidentally spoiling the alignment of data in the file.
> There are special commands for insertion.
> 
> (I copied this from git master just to be sure!)
> 
> The list of commands underneath list several commands that have "insert" in 
> their name, leading the naive
> reader (me) to believe they will insert rather than overwrite.
> 
> However, this is not the case: the various keystrokes listed underneath which 
> mention "insert" all overstrike.
> 
> I suspect that my confusion results from guessing (incorrectly) that the 
> sentence "There are special
> commands for insertion" uses the word "insertion" to oppose "overwrite" 
> earlier in the paragraph; but in fact, it
> means "insertion" in the sense of "inserting a character", which happens 
> always to overwrite in hexl-mode.

Thanks, I clarified this text.