Change license header to a one-line ‘SPDX-License-Identifier’.

This change implements the consensus reached in the group.

Changes were made with this ed script:

  # Match the first empty line.
  /^$
  # Delete everything up to that line.
  1,.d
  # Insert the header.
  i
  ;;; SPDX-License-Identifier: GPL-3.0-or-later

  .
  # Done.
  wq

Fixes: guix-science/guix-science#196

1 files changed, 21 insertions, 0 deletions

diff --git a/README.rst b/README.rst
index d5d6915..17459cf 100644
--- a/README.rst
+++ b/README.rst
@@ -41,9 +41,30 @@ using:
 
 .. _Getting Substitutes from Other Servers: https://guix.gnu.org/manual/en/guix.html#Getting-Substitutes-from-Other-Servers
 
+.. _licensing:
+
+Licensing
+---------
+
+Like Guix itself, Guix-Science is distributed under the terms of the `GNU
+General Public License`, version 3 or (at your option) any later
+version.
+
+A copy of the license is included in the ``COPYING`` file, and each
+source file contains an `SPDX header` confirming its license.
+
+Copyright is held by the diverse group of copyright holders for the many
+contributions made to Guix-Science over time.
+
+.. _GNU General Public License_: https://www.gnu.org/licenses/gpl-3.0
+.. _SPDX header_: https://spdx.dev/learn/handling-license-info/
+
 Contributing
 ------------
 
+Contributors agree to provide their changes under the same license as
+the rest of Guix-Science—see :ref:`licensing`.
+
 We accept software fulfilling the following criteria:
 
 - `Free and open source`_. Use guix-science-nonfree_ otherwise.