Use "git" instead of "CVS" in the description of the bison-patches mailing list

[Stefano Lattarini]

In the mailing list description here:

  <https://lists.gnu.org/mailman/listinfo/bison-patches>

I read:

  ``If you have found a bug in Bison, or have made an improvement, please
    send a patch, made for the CVS sources, to this mailing list.''

But bison doesn't use CVS anymore (thanks $DEITY :-) so that a correct
description should refer to the "git sources" or "git repository" (and
a link to said repository wouldn0t hurt either, IMHO).

Regards,
  Stefano