Added links in README.md to mailing lists.

This will make it easier for prospective users and developers to
locate the mailman lists.

README.md

@@ -59,7 +59,9 @@ For the player only:
 The provided build system is the GNU automake/autoconf system, and
 the main library, libtheora, should already build smoothly on any
 system.  Failure of libtheora to build on a GNU-enabled system is
-considered a bug; please report problems to theora-dev@xiph.org.
+considered a bug; please report problems to theora-dev@xiph.org,
+https://lists.xiph.org/mailman/listinfo/theora-dev or preferrably to
+https://gitlab.xiph.org/xiph/theora.
 
 Windows build support is included in the win32 directory.
 
@@ -67,6 +69,9 @@ Project files for Apple XCode are included in the macosx directory.
 
 There is also a more limited scons build.
 
+The mailing list theora@xiph.org has been created for discussing use
+of the theora video codec, https://lists.xiph.org/mailman/listinfo/theora.
+
 ### How do I use the sample encoder?
 
 The sample encoder takes raw video in YUV4MPEG2 format, as used by