Add an entry for the AVFilterContext.description addition.

Originally committed as revision 20355 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -12,6 +12,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2009-10-23 - r20354 - lavfi 1.4.0 - AVFilterContext.description
+  Add a description field to AVFilterContext.
+
 2009-10-19 - r20302 - lavfi 1.3.0 - avfilter_make_format_list()
   Change the interface of avfilter_make_format_list() from
   avfilter_make_format_list(int n, ...) to