chore: add script for creating signed merge commits

Merge messages are composed of PR number + appended shortlog.
Script is supposed to work only if there are no merge conflicts.

Example usage: `./merge-pr.sh 1234`

merge-pr.sh

@@ -0,0 +1,54 @@
+#!/bin/bash
+#
+#    Copyright © 2016 Zetok Zalbavar
+#
+#    This program is 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, either version 3 of the License, or
+#    (at your option) any later version.
+#
+#    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
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Script for merging pull requests. Works only when there are no merge
+# conflicts. Assumes that working dir is a qTox git repo.
+#
+# Requires SSH key that github accepts and GPG set to sign merge commits.
+
+# usage:
+#   ./$script $pr_number
+
+PR=$1
+
+# FIXME: ↓
+#[[ ${PR} =~ "^[:digit:]+$" ]] || echo "Not a PR number!" && exit 1
+
+# list remotes, and if there's no tux3 one, add it
+if  ! git remote | grep original
+then
+    git remote add original git@github.com:tux3/qTox.git
+fi
+
+git fetch original && \
+git checkout master && \
+git rebase original/master master && \
+git fetch original pull/$PR/head:$PR && \
+git checkout master -b merge$PR && \
+git merge --no-ff -S $PR -m "Merge pull request #$PR
+
+$(git shortlog master..$PR)" && \
+echo ""
+echo "PR #$PR was merged into «merge$PR» branch."
+echo "To compare with master:"
+echo "git diff master..merge$PR"
+echo ""
+echo "To push that to master on github:"
+echo "git checkout master && git merge --ff merge$PR && git push original master"
+echo ""
+echo "After pushing to master, delete branches:"
+echo "git branch -d {merge,}$PR"