doc/general.texi: clarify FDK-AAC licensing & usability

Mnetion it can be used to decode as well.

doc/general.texi

@@ -46,9 +46,10 @@ upgrade FFmpeg's license to LGPL version 3 (or if you have enabled
 GPL components, GPL version 3) by passing @code{--enable-version3} to configure in
 order to use it.
 
-The Fraunhofer AAC library is licensed under a license incompatible to the GPL
-and is not known to be compatible to the LGPL. Therefore, you have to pass
-@code{--enable-nonfree} to configure to use it.
+The license of the Fraunhofer AAC library is incompatible with the GPL.
+Therefore, for GPL builds, you have to pass @code{--enable-nonfree} to
+configure in order to use it. To the best of our knowledge, it is
+compatible with the LGPL.
 @end float
 
 @subsection OpenCORE AMR
@@ -71,7 +72,7 @@ Then pass @code{--enable-libvo-amrwbenc} to configure to enable it.
 
 @subsection Fraunhofer AAC library
 
-FFmpeg can make use of the Fraunhofer AAC library for AAC encoding.
+FFmpeg can make use of the Fraunhofer AAC library for AAC decoding & encoding.
 
 Go to @url{http://sourceforge.net/projects/opencore-amr/} and follow the
 instructions for installing the library.