add release helper scripts

scripts/release

@@ -0,0 +1,2 @@
+python setup.py register sdist upload --identity="Thomas Waldmann" --sign
+

scripts/sign-binaries

@@ -0,0 +1,9 @@
+#!/bin/bash
+# usage: sign-binaries 201512312359
+
+for file in dist/borg-*; do
+    gpg --armor --detach-sign $file
+done
+
+touch -t $1 dist/*
+