Added a README to the keys directory

keys/README.md

@@ -0,0 +1,10 @@
+# Insecure Keypair
+
+These keys are the "insecure" public/private keypair we offer to
+[base box creators](http://vagrantup.com/docs/base_boxes.html) for use in their base boxes so that
+vagrant installations can automatically SSH into the boxes.
+
+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`