Update README.md to include primary cluster variables.

Author: nichollri

Terraform/fsxn-replicate/README.md

@@ -9,6 +9,29 @@ You will need to define some key characteristics of your destination FSxN cluste
 
 These values can be found in the following variables files: Primary_FSxN_variables.tf and DR_FSxN_variables.tf
 
+## Prerequisites
+You have an existing FSx ONTAP system that you want to replicate to a new FSxN system.  There is proper networking connectivy between the source FSxN system and the region/VPC/subnets where the destination FSxN system will be deployed.
+
+SnapMirror replication requires **ICMP** and ports **11104** and **11105**.
+
+## Primary Inputs
+
+| Name                  | Description                                                                                                   | Type           | Default                              | Required |
+| --------------------- | ------------------------------------------------------------------------------------------------------------- | -------------- | ------------------------------------ | :------: |
+| prime_hostname        | Hostname or IP address of primary cluster.                                                                    | `string`       |                                      |   Yes    |
+| prime_fsxid           | FSx ID of the primary cluster.                                                                                | `string`       |                                      |   Yes    |
+| prime_clus_name       | This is the name of the cluster given for ONTAP TF connection profile.  This is a user created value, that can be any string.  It is referenced in many ONTAP TF resources | `string`  |  primary_clus  |   Yes   | 
+| prime_svm             | Name of the primary SVM for the volumes that will be replicated.                                              | `string`       |                                      |   Yes    |
+| prime_cluster_vserver | Name of the ONTAP cluster vserver for intercluster LIFs in the primary cluster.  Can be found by running `network interface show` on the primary cluster. It will have the format FsxId#################  | `string` |  Yes  |
+| prime_aws_region      | AWS region of the primary FSx ONTAP system                                                                    | `string`       |                                      |  Yes     |
+| username_pass_secrets_id | Name of the secrets ID in AWS secrets.  The AWS Secret should has format of a key `username` which should be fsxadmin and a key `password` and the password of the FSxN | `string` |   | Yes |
+| validate_certs        | Do we validate the cluster certs (true or false)                                                              | `string`       | false                                |  No      |
+| list_of_volumes_to_replicate | List of volume names to replicate to the destination FSx ONTAP system                                  | `list(string)`   |                                      |  Yes     |
+
+
+ 
+
+
 
 
 ## Author Information