Docs: Fix missing required option `ami_name` for ebssurrogate builder

website/source/docs/builders/amazon-ebssurrogate.html.md.erb

@@ -38,6 +38,11 @@ builder.
 -   `access_key` (string) - The access key used to communicate with AWS. [Learn
     how to set this](/docs/builders/amazon.html#specifying-amazon-credentials)
 
+-   `ami_name` (string) - The name of the resulting AMI that will appear when
+    managing AMIs in the AWS console or via APIs. This must be unique. To help
+    make this unique, use a function like `timestamp` (see [template
+    engine](../templates/engine.html) for more info).
+
 -   `instance_type` (string) - The EC2 instance type to use while building the
     AMI, such as `m1.small`.
 
@@ -591,4 +596,4 @@ volumes created by this builder, any volumes inn the source AMI which are not
 marked for deletion on termination will remain in your account.
 
 
-<%= partial "partials/builders/aws-ssh-differentiation-table" %>
+<%= partial "partials/builders/aws-ssh-differentiation-table" %>