add script to release binaries for all platforms

.gitignore

@@ -1 +1,2 @@
 /selfupdate-example
+/release

cmd/selfupdate-example/make-release.sh

@@ -0,0 +1,21 @@
+#! /bin/bash
+
+set -e
+
+if [ ! -d .git ]; then
+    echo 'Run this script from root of repository' 1>&2
+    exit 1
+fi
+
+command=selfupdate-example
+
+rm -rf release
+gox -verbose ./cmd/$command
+mkdir -p release
+mv selfupdate-example_* release/
+cd release
+for bin in *; do
+    mv "$bin" "$command"
+    zip "${bin}.zip" "$command"
+    rm "$command"
+done