fix: missing install name (#25)

`helm install` need specified name or generated.
```shell
must either provide a name or specify --generate-name
```

README.md

@@ -11,7 +11,7 @@ See the cert-manager's documentation for more details on webhook : https://cert-
 ```
 helm repo add cert-manager-alidns-webhook https://devmachine-fr.github.io/cert-manager-alidns-webhook
 helm repo update
-helm install cert-manager-alidns-webhook/alidns-webhook
+helm install alidns-webhook cert-manager-alidns-webhook/alidns-webhook
 ```
 
 Create the secret holding alibaba credential :