bug#36365: Add info how to deselect secondary selection (Emacs manual)

[Sebastian Urban <mrsebastianurban@gmail.com>]

>> But I see nothing wrong with the doc string as it is.
>
> Right now the string is:
>    Set one end of the secondary selection to the position clicked
>    on.  Use <M-mouse-3> to set the other end and complete the
>    secondary selection.
>
> As you can see - no information about deselect, so perhaps just
> copy-paste last sentence from your patch - "This command
> cancels any existing secondary selection, when it starts a new
> one."

Any update on this...

>> I see now that there's no way of cancelling a secondary selection
>> without starting a new one.  So I changed the text to reflect that.
>
> Alright, but I think:
>    use @kbd{M-mouse-3} to set the other end and complete the
>    selection.
>
> that this sentence from the patch is unnecessary.  How to set
> secondary selection is in description of 'M-mouse-3' which is just
> ONE line below.  In doc string of 'mouse-start-secondary' it is OK,
> because there is no description of 'M-mouse-3', but in the manual
> there is.

and this?