Update index.html.markdown

Added a note about self-signed certs and vsphere.

website/source/docs/providers/vsphere/index.html.markdown

@@ -28,6 +28,8 @@ provider "vsphere" {
   user           = "${var.vsphere_user}"
   password       = "${var.vsphere_password}"
   vsphere_server = "${var.vsphere_server}"
+  # if you have a self-signed cert
+  allow_unverified_ssl = true
 }
 
 # Create a folder