add capnp and ffmpeg (#4)

setup.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [ "$(uname)" = "Darwin" ]; then
+  brew install nasm pkg-config
+else
+  sudo apt-get update && sudo apt-get install -y nasm cmake g++ pkg-config
+fi