gst-ffmpeg: expand package description to describe libav usage

- Change URL to gst-ffmpeg page at the gstreamer site.
- Note that gst-ffmpeg actually uses libav, not ffmpeg [anymore].
- Note that gst-ffmpeg is using an internal copy of libav, not a
  system copy.

Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Acked-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gstreamer/gst-ffmpeg/Config.in

@@ -4,9 +4,14 @@ config BR2_PACKAGE_GST_FFMPEG
 	depends on BR2_LARGEFILE
 	depends on BR2_INET_IPV6
 	help
-	  GStreamer plugin using FFmpeg.
+	  GStreamer plugin containing one plugin with a set of elements using
+	  the Libav library.  It contains most popular decoders as well as
+	  colorspace conversion elements.
 
-	  http://gstreamer.freedesktop.org/
+	  This package is configured to use an internal copy of the Libav
+	  library.
+
+	  http://gstreamer.freedesktop.org/modules/gst-ffmpeg.html
 
 if BR2_PACKAGE_GST_FFMPEG