docs(README): add installation instructions for docker.gitea.com (#817)

Follow-up to https://gitea.com/gitea/helm-chart/pulls/814 and https://gitea.com/gitea/blog/pulls/429.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/817
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-committed-by: justusbunsi <sk.bunsenbrenner@gmail.com>

.markdownlint.yaml

@@ -129,6 +129,7 @@ MD041:
 MD044:
   # List of proper names
   names:
+    - docker.gitea.com
     - Gitea
     - PostgreSQL
     - Memcached

README.md

@@ -140,6 +140,12 @@ Alternatively, the chart can also be installed from Dockerhub (since v9.6.0)
 helm install gitea oci://registry-1.docker.io/giteacharts/gitea
 ```
 
+To avoid potential Dockerhub rate limits, the chart can also be installed via [docker.gitea.com](https://blog.gitea.com/docker-registry-update/) (since v9.6.0)
+
+```sh
+helm install gitea oci://docker.gitea.com/charts/gitea
+```
+
 When upgrading, please refer to the [Upgrading](#upgrading) section at the bottom of this document for major and breaking changes.
 
 ## High Availability