COPYING,LICENSE: include GPLv3+ license text with the package

If you're redistributing this package or a derivative work, the GPLv3
says that you should include a copy of the license along with it. To
make life easier for packagers and developers, we include the text of
the GPLv3 in a new LICENSE file. A new COPYING file then elaborates
that you can use either the GPLv3, or any later version.

Author: orlitzky

COPYING

@@ -0,0 +1,15 @@
+conway-polynomials - a python interface to Frank Lübeck's Conway polynomial database
+Copyright (C) 2023 The Sage Developers
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.