docs: added usage example

Signed-off-by: leonsteinhaeuser <[email protected]>

README.md

@@ -22,6 +22,22 @@ chart:
   release_name: <chart_release_name>   # e.g. background-develop
 ```
 
+## Usage
+
+```hcl
+provider "argocd" {
+  server_addr = "argo.example.com"
+  auth_token  = "my-token"
+  grpc_web    = true
+}
+
+module "namespace-management" {
+  source  = "tagesspiegel/application-set/argocd"
+  version = "1.0.0"
+  # insert the required variable here
+}
+```
+
 ## Cluster selection
 
 The cluster selection is based on the ``
@@ -72,4 +88,3 @@ No modules.
 
 No outputs.
 <!-- END_TF_DOCS -->
-