add contributing link

Simon Stier · web-flow · commit 9323ba73c4c4 · 2023-09-15T16:07:16.000+02:00
diff --git a/README.md b/README.md
@@ -76,3 +76,7 @@ for record set creation.
     ```bash
     make lint
     ```
+
+## Contribute
+see [CONTRIBUTING.md](https://github.com/stackitcloud/certbot-dns-stackit/blob/main/CONTRIBUTING.md)
+
