add docs for stackit webhook

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

content/docs/configuration/acme/dns01/README.md

@@ -181,6 +181,7 @@ Links to these supported providers along with their documentation are below:
 - [`cert-manager-webhook-netcup`](https://github.com/aellwein/cert-manager-webhook-netcup)
 - [`cert-manager-webhook-pdns`](https://github.com/zachomedia/cert-manager-webhook-pdns)
 - [`cert-manager-webhook-zilore`](https://gitlab.com/zilore/cert-manager-webhook-zilore)
+- [`stackit-cert-manager-webhook`](https://github.com/stackitcloud/stackit-cert-manager-webhook)
 
 You can find more information on how to configure webhook providers [here](./webhook.md).