Added readme for the cross-region example

Author: yasinbaskan

terraform/adb_with_cross-region_standby/README.md

@@ -0,0 +1,31 @@
+# Autonomous AI Database with a cross-region standby
+
+This Terraform example creates an Autonomous AI Database with a cross-region standby.
+
+You can run it by updating the file _terraform.tfvars_ file with the settings you want. 
+
+Enter your tenancy OCID, user OCID, user fingerprint, private key file path, region name, and compartment OCID. Change the other settings like database name and compute count to your liking.
+
+```tenancy_ocid     = ""
+user_ocid        = ""
+fingerprint      = ""
+private_key_path = ""
+
+compartment_ocid = ""
+
+primary_region = "us-ashburn-1"
+standby_region = "us-phoenix-1"
+
+adb_display_name = "primarydb"
+adb_db_name      = "primarydb"
+
+admin_password = "WelcomeADB26"
+  
+db_workload = "OLTP"
+
+compute_count = 2
+data_storage_size_in_tbs = 1
+```
+
+
+