Update doc on Vagrant local override file

docs/vagrant.md

@@ -40,10 +40,30 @@ k8s-02    Ready     45s
 k8s-03    Ready     45s
 ```
 
+Customize Vagrant
+=================
+
+You can override the default settings in the `Vagrantfile` either by directly modifying the `Vagrantfile`
+or through an override file.
+
+In the same directory as the `Vagrantfile`, create a folder called `vagrant` and create `config.rb` file in it.
+
+You're able to override the variables defined in `Vagrantfile` by providing the value in the `vagrant/config.rb` file,
+e.g.:
+
+    echo '$forwarded_ports = {8001 => 8001}' >> vagrant/config.rb
+
+and after `vagrant up` or `vagrant reload`, your host will have port forwarding setup with the guest on port 8001.
+
 Use alternative OS for Vagrant
 ==============================
 
 By default, Vagrant uses Ubuntu 16.04 box to provision a local cluster. You may use an alternative supported
-operating system for your local cluster. Change `$os` variable in `Vagrantfile` to another operating system to change
-the vagrant base box. The supported operating systems for vagrant are defined in the `SUPPORTED_OS` constant in
-the `Vagrantfile`.
+operating system for your local cluster.
+
+Customize `$os` variable in `Vagrantfile` or as override, e.g.,:
+
+    echo '$os = "coreos-stable"' >> vagrant/config.rb
+
+
+The supported operating systems for vagrant are defined in the `SUPPORTED_OS` constant in the `Vagrantfile`.