Add usage section (as suggested via #29, thanks @mikl!)

README.md

@@ -28,6 +28,18 @@ Inspired by Robert C. Martin's book, [Clean Code](https://www.investigatii.md/up
   objects in your Kubernetes cluster (e.g. generated by the Kustomize [secretGenerator](
   https://kubectl.docs.kubernetes.io/pages/reference/kustomize.html#secretgenerator))
 
+## Usage
+
+```console
+seiso --help
+```
+```console
+seiso image --help
+seiso image history --help
+seiso image orphans --help
+seiso configmaps --help
+seiso secrets --help
+```
 
 ## Why should I use this tool?