fix: use bash for install script (#44)

Use bash for the install script instead of sh. The KTF install script
relies on some bash-specific shell builtins (set -o pipefail) and won't
run with plain sh.

docs/install.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 set -euo pipefail