(DOCS-7017) Add site information (#16585)

* (DOCS-7017) Add site information

* (DOCS-7017) Correct URL

* Update terraform/README.md

Co-authored-by: May Lee <[email protected]>

---------

Co-authored-by: May Lee <[email protected]>

terraform/README.md

@@ -12,8 +12,8 @@ The Datadog Terraform provider is available through the [Terraform Registry][1].
 
 ### Configuration
 
-1. [Install Terraform][2]
-2. Create a directory to contain the Terraform configuration files, for example: `terraform_config/`
+1. [Install Terraform][2].
+2. Create a directory to contain the Terraform configuration files, for example: `terraform_config/`.
 3. Create a `main.tf` file in the `terraform_config/` directory with the following content:
     ```
     terraform {
@@ -31,6 +31,11 @@ The Datadog Terraform provider is available through the [Terraform Registry][1].
     }
     ```
 
+    **Note**: If you are not using the Datadog US1 site, you must set the `api_url` [optional parameter][7] with your [Datadog site][6]. Ensure the documentation site selector on the right of the page is set to your correct Datadog site, then use the following URL as the value of the `api_url` parameter:
+
+    ```
+    https://api.{{< region-param key="dd_site" code="true" >}}/
+    ```
 4. Run `terraform init`. This initializes the directory for use with Terraform and pulls the Datadog provider.
 5. Create any `.tf` file in the `terraform_config/` directory and start creating Datadog resources. 
 
@@ -102,4 +107,6 @@ Need help? Contact [Datadog support][3].
 [2]: https://learn.hashicorp.com/tutorials/terraform/install-cli
 [3]: https://docs.datadoghq.com/help/
 [4]: https://github.com/DataDog/datadogpy
-[5]: https://docs.datadoghq.com/monitors/types/process/
+[5]: https://docs.datadoghq.com/monitors/types/process/
+[6]: https://docs.datadoghq.com/getting_started/site/
+[7]: https://registry.terraform.io/providers/DataDog/datadog/latest/docs#optional