Clarify licensing information about files borrowed from libjpeg.

LICENSE

@@ -20,8 +20,12 @@ Specifically, the GPL parts of Libav are
 
 There are a handful of files under other licensing terms, namely:
 
-* The files libavcodec/jfdctfst.c, libavcodec/jfdctint.c, libavcodec/jrevdct.c
-  are taken from libjpeg, see the top of the files for licensing details.
+* The files libavcodec/jfdctfst.c, libavcodec/jfdctint_template.c and
+  libavcodec/jrevdct.c are taken from libjpeg, see the top of the files for
+  licensing details. Specifically note that you must credit the IJG in the
+  documentation accompanying your program if you only distribute executables.
+  You must also indicate any changes including additions and deletions to
+  those three files in the documentation.
 
 Should you, for whatever reason, prefer to use version 3 of the (L)GPL, then
 the configure parameter --enable-version3 will activate this licensing option