Documentation: Adding playlist files to playlist buffer

[Scarlett McAllister]

Hello! I have a teeny documentation patch to share. It took me a while 
to figure out how to get a saved playlist's contents back into a buffer. 
So this small note should hopefully avoid similar time sinks by other 
newbies by making mention of the correct function in the manual!

> @defun emms-play-playlist file
> Add files from a playlist file to the current playlist buffer.
>
> diff --git a/doc/emms.texinfo b/doc/emms.texinfo
> index da9aee2..9762aea 100644
> --- a/doc/emms.texinfo
> +++ b/doc/emms.texinfo
> @@ -946,6 +946,9 @@ Store the current playlist to FILE as the type 
> FORMAT.  The default
>  format is specified by @var{emms-source-playlist-default-format}.
>  @end defun
>
> +@defun emms-play-playlist file
> +Add files from a playlist file to the current playlist buffer.
> +
>  The current Emms playlist buffer is stored in the variable
>  @var{emms-playlist-buffer}.

Scarlett