fix command formatting in readme

Signed-off-by: Kairo de Araujo <[email protected]>

README.md

@@ -11,7 +11,7 @@ Helm's [documentation](https://helm.sh/docs) to get started.
 
 Once Helm has been set up correctly, add the repo as follows:
 
-  helm repo add rstuf https://repository-service-tuf.github.io/helm-charts
+    helm repo add rstuf https://repository-service-tuf.github.io/helm-charts
 
 If you had already added this repo earlier, run `helm repo update` to retrieve
 the latest versions of the packages.  You can then run `helm search repo