Add distribution README

Limit retention

.github/workflows/ci.yaml

@@ -39,7 +39,9 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: tkey-libs
+          retention-days: 2
           path: |
+            README-DIST.txt
             app.lds
             LICENSE
             include/*

README-DIST.txt

@@ -0,0 +1,31 @@
+tkey-libs binary distribution
+
+This is the binary distribution of:
+
+  https://github.com/tillitis/tkey-libs
+
+You should be able to use this distribution directly in device apps
+simply by pointing LIBDIR to where you unpacked this archive:
+
+  make LIBDIR=~/Download/tkey-libs
+
+Copyright Tillitis AB.
+
+These programs are 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, version 2 only.
+
+These programs are distributed in the hope that they 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
+
+See LICENSE for the full GPLv2-only license text.
+
+Note that Monocypher is Copyright Loup Vaillant and released under CC0
+1.0 Universal, see monocypher/LICENSE.

tools/spdx-ensure

@@ -20,6 +20,7 @@ missingok_files=(
 LICENSE
 Makefile
 README.md
+README-DIST.txt
 RELEASE.md
 example-app/Makefile
 monocypher/LICENSE