Remove reference to PPK in keys readme

keys/README.md

@@ -8,10 +8,3 @@ If you're working with a team or company or with a custom box and
 you want more secure SSH, you should create your own keypair
 and configure the private key in the Vagrantfile with
 `config.ssh.private_key_path`
-
-# Putty
-
-If you are using Vagrant on windows, the .ppk file contained here, in the keys directory,
-has been generated from the private key and should be used to connect Putty to any VMs that 
-are leveraging the default key pair. See [guide](http://docs.vagrantup.com/v1/docs/getting-started/ssh.html) 
-in the documentation for more details on using Putty with Vagrant.