README: add licensing information

Now that we are moving away from boilerplate code towards SPDX license
tags in individual file headers, we should have a short note about what
these tags mean. Also, until now, there was effectively no explicit
information that barebox is licensed under GPLv2 (only). This could have
been interpolated from the existence of a GPLv2 text in ./COPYING (and
from most of the individual file headers… have fun reading all of them),
but a warranty and copyright notice was still missing. Add those as a
catch-all for the project to ease application of GPLv2 article 0:

      0. This License applies to any program or other work which contains
    a notice placed by the copyright holder saying it may be distributed
    under the terms of this General Public License. […]

and article 1:

      1. You may copy and distribute verbatim copies of the Program's
    source code as you receive it, in any medium, provided that you
    conspicuously and appropriately publish on each copy an appropriate
    copyright notice and disclaimer of warranty; […]

Since barebox goes back to U-Boot, I tried to find explicit project-wide
copyright lines, but the only one I could find was the one from U-Boot's
old README in commit 7e149c897b95b40752. If there are additional
copyright holders, those are probably only present in the respective
file headers.

Signed-off-by: Roland Hieber <rhi@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 32 insertions, 0 deletions

diff --git a/README b/README
index 940e1f96dd..dada97cab3 100644
--- a/README
+++ b/README
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
 Barebox
 -------
 
@@ -222,3 +224,33 @@ are the release rules:
   does never change, in order to make life easier for distribution
   people.
 
+
+License
+-------
+
+Copyright (C) 2000 - 2005 Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+Copyright (C) 2018 Sascha Hauer, Pengutronix, and individual contributors
+
+Barebox is free software: you can redistribute it and/or modify it under the
+terms of the GNU General Public License, version 2, as published by the Free
+Software Foundation.
+
+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 in the file
+COPYING along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+Individual files may contain the following SPDX license tags as a shorthand for
+the above copyright and warranty notices:
+
+    SPDX-License-Identifier: GPL-2.0-only
+    SPDX-License-Identifier: GPL-2.0-or-later
+
+This eases machine processing of licensing information based on the SPDX
+License Identifiers that are available at http://spdx.org/licenses/.
+
+Also note that some files in the Barebox source tree are available under
+several different GPLv2-compatible open-source licenses. This fact is noted
+clearly in the file headers of the respective files.