[PATCH 2/2] LICENSE: add SPDX identifiers

[Paul Spooren]

SPDX license header follow a machine readable and versioned identifier
format for licenses. The adoption to such system would simplify
scanning of licenses within OpenWrt.

Adopted from the Linux Kernel[0] store store SPDX identifiers at the
top of the LICENSE file.

Both the `GPL-2.0` and `GPL-2.0+` identifiers are deprecated[1] and are
in contrast to the Linux Kernel not added. When adding such headers it
should be the latest SPDX version.

[0]: https://github.com/torvalds/linux/commit/255247c2770ada6edace04173b35307869b47d99
[1]: https://spdx.org/licenses/

Signed-off-by: Paul Spooren <mail at aparcar.org>
---
 LICENSE | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/LICENSE b/LICENSE
index d159169d10..687bdddb11 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,3 +1,16 @@
+Valid-License-Identifier: GPL-2.0-only
+Valid-License-Identifier: GPL-2.0-or-later
+SPDX-URL: https://spdx.org/licenses/GPL-2.0.html
+Usage-Guide:
+  To use this license in source code, put one of the following SPDX
+  tag/value pairs into a comment according to the placement
+  guidelines in the licensing rules documentation.
+  For 'GNU General Public License (GPL) version 2 only' use:
+    SPDX-License-Identifier: GPL-2.0-only
+  For 'GNU General Public License (GPL) version 2 or any later version' use:
+    SPDX-License-Identifier: GPL-2.0-or-later
+License-Text:
+
                     GNU GENERAL PUBLIC LICENSE
                        Version 2, June 1991
 
-- 
2.25.1