docs: Add note about the EC Terraform provider (#534)

Mentions the EC Terraform provider as the preferred tool to manage
deployments.

Signed-off-by: Marc Lopez Rubio <marc5.12@outlook.com>

Author: marclop

README.md

@@ -8,6 +8,8 @@ The goal of this project is to provide an easier way to interact with the Elasti
 
 To get started with Elastic Cloud Control, see the [official documentation](https://www.elastic.co/guide/en/ecctl/current/index.html).
 
+_NOTE: While it's posibble to create and manage deployments through ecctl, the [Elastic Cloud Terraform provider](https://github.com/elastic/terraform-provider-ec) provides a better interface._
+
 ## Contributing
 
 If you are interested in becoming a part of this project, take a look at our [contribution guidelines](./CONTRIBUTING.md).