Move release script to briar-debian

briar-debian!1

tools/release-briar-headless.sh

-#!/usr/bin/env bash
-# Copyright (c) 2019 Nico Alt
-# SPDX-License-Identifier: AGPL-3.0-only
-# License-Filename: LICENSE.md
-
-set -e -x
-
-cd ../briar-android
-
-./gradlew --configure-on-demand briar-headless:jar
-
-cd briar-headless/build/libs
-
-sha256sum briar-headless.jar > sha256sum.txt
-git log | head -n 1 > commit.txt
-
-echo "To sign, call 'for file in \$(ls); do gpg -b \"\$file\"; done'"
-
-xdg-open .