feat: Include README with requirments, API and usage example

charms/argo-controller/terraform/README.md

@@ -1,3 +1,50 @@
 # Terraform module for argo-controller
 
-This is a Terraform module facilitating the deployment of argo-controller charm, using the [Terraform juju provider](https://registry.terraform.io/providers/juju/juju/latest/docs).
+This is a Terraform module facilitating the deployment of argo-controller charm, using the [Terraform juju provider](https://github.com/juju/terraform-provider-juju/). For more information, refer to the provider [documentation](https://registry.terraform.io/providers/juju/juju/latest/docs). 
+
+## Requirements
+This module requires a `juju` model to be available. Refer to the [usage section](#usage) below for more details.
+
+## Inputs
+The module offers the following configurable inputs:
+
+| Name | Type | Description | Required |
+| - | - | - | - |
+| `app_name`| string | Application name | False |
+| `channel`| string | Channel that the charm is deployed from | False |
+| `config`| map(string) | Map of the charm configuration options | False |
+| `model_name`| string | Name of the model that the charm is deployed on | True |
+| `resources`| map(number) | Map of charm resources revisions | False |
+| `revision`| number | Revision number of the charm name | False |
+
+## Outputs
+Upon applied, the module exports the following outputs:
+
+| Name | Description |
+| - | - |
+| `app_name`|  Application name |
+| `provides`| Map of `provides` endpoints |
+| `requires`|  Map of `reqruires` endpoints |
+
+## Usage
+
+### Integrating in a higher-level module
+In order to use this module in a higher-level module, ensure that Terraform is aware of its `model` dependency by passing to the `model_name` input the value of the output `juju_model.<model_label>.name`. For example:
+
+```
+resource "juju_model" "kubeflow" {
+  name = kubeflow
+}
+
+module "argo-controller" {
+  source = "<path-to-this-directory>"
+  model_name = juju_model.kubeflow.name
+}
+```
+
+### Applying directly the module from the CLI
+Although not recommended, in order to apply the module directly from the CLI, ensure that a `juju` model has already been created and then manually use its name as the value of the `model_name` input. For example:
+```
+# check that there is a model called `kubeflow`
+terraform apply -var "model_name=kubeflow"
+```