Add post-install script

Signed-off-by: Severin Kaderli <severin.kaderli@gmail.com>

post-install.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+#
+# This is the post installation script. This should be executed only after
+# install.sh has been executed completly and the system has been rebooted
+# after that.
+#
+# This script installs npm packages.
+#
+# Author: Severin Kaderli <severin.kaderli@gmail.com>
+# Usage: ./post-install.sh
+. utils.sh
+
+#######################################
+# Configuration variables
+#######################################
+# Array of npm packages which should be installed globally
+NPM_PACKAGES=(
+    "@vue/cli"
+    "gatsby-cli"
+    "npm-check-updates"
+)
+
+#######################################
+# Main code
+#######################################
+# Install global npm packages
+print_header "Installing global npm packages"
+npm i -g "${NPM_PACKAGES[@]}"