README.md in infrataster-0.1.5 vs README.md in infrataster-0.1.6

@@ -26,11 +26,11 @@
 
 Create Vagrantfile:
 
 ```ruby
 # Vagrantfile
-Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
+Vagrant.configure("2") do |config|
   config.vm.box = "hashicorp/precise64"
 
   config.vm.define :proxy do |c|
     c.vm.network "private_network", ip: "192.168.33.10"
     c.vm.network "private_network", ip: "171.16.33.10", virtualbox__intnet: "infrataster-example"
@@ -144,9 +144,28 @@
 Infrataster::Server.define(
   # ...
   ssh: {host: 'hostname', user: 'testuser', keys: ['/path/to/id_rsa']}
 )
 ```
+
+### #ssh_exec
+
+You can execute a command on the server like the following:
+
+```ruby
+describe server(:proxy) do
+  let(:time) { Time.now }
+  before do
+    current_server.ssh_exec "echo 'Hello' > /tmp/test-#{time.to_i}"
+  end
+  it "executes a command on the current server" do
+    result = current_server.ssh_exec("cat /tmp/test-#{time.to_i}")
+    expect(result.chomp).to eq('Hello')
+  end
+end
+```
+
+This is useful to test cases which depends on the status of the server.
 
 ## Resources
 
 "Resource" is what you test by Infrataster. For instance, the following code describes `http` resource.