Add COPYING and license as MIT-0

This is just proof of concept code, so make it as free-as-in-speech as
is reasonable.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

COPYING

diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..9c5dd0f
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,18 @@
+The MIT-Zero License
+
+Copyright (c) <year> <copyright holders>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

main.py

diff --git a/main.py b/main.py
index 065729d..c160859 100755
--- a/main.py
+++ b/main.py
@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+# Copyright (C) 2020 by the Linux Foundation
+# SPDX-License-Identifier: MIT-0
 import sys
 import os
 import base64

verify-all.sh

diff --git a/verify-all.sh b/verify-all.sh
index fd72ffd..228b82e 100755
--- a/verify-all.sh
+++ b/verify-all.sh
@@ -4,6 +4,10 @@
 #  python3 -mvenv .venv
 #  source .venv/bin/activate
 #  pip install -r requirements.txt
+#
+# Copyright (C) 2020 by the Linux Foundation
+# SPDX-License-Identifier: MIT-0
+#
 echo "--------- UNHASHED (expected to fail) ---------"
 ./main.py -m emails/unsigned.eml verify
 echo