feat: update README with a basic example usage and references (#36)

Author: david-montano-circleci

README.md

@@ -1,6 +1,35 @@
 # CircleCI Terraform Provider
 The CircleCI Terraform Provider enable customers to manage CircleCI projects with IaC patterns, matching the same patterns used to manage GitHub repos. For large-scale organizations, this enables automated project creation for new teams or projects.
 
+## Usage
+The current documentation is found [here](https://registry.terraform.io/providers/CircleCI-Public/circleci/latest/docs).
+Define the provider:
+```hcl
+terraform {
+  required_providers {
+    circleci = {
+      source = "CircleCI-Public/circleci"
+      version = "0.1.1"
+    }
+  }
+}
+
+provider "circleci" {
+  host = "https://circleci.com/api/v2/"
+  #key  = "*****" # here you set you CircleCI API Key
+}
+```
+Start defining Data Sources and Resources. For example:
+```hcl
+resource "circleci_project" "test_project" {
+  name 				= "Project_Name"
+  project_provider 	= "github"
+  organization_id 	= "********-****-****-****-****************"
+}
+```
+
+Use the Official [CircleCI API documentation](https://circleci.com/docs/api/v2/index.html) to check which valid values might be needed for some resources.
+
 ## Upcoming Features in the Next Release
 
 - Import existing resources