docs(README): add workaround for rotating TLS certificates (#907)

The following patch extends the README of an additional chapter, how to handle
rotating TLS certificates mounted as secret into the container filesystem.

Reviewed-on: https://gitea.com/gitea/helm-gitea/pulls/907
Reviewed-by: pat-s <pat-s@noreply.gitea.com>
Co-authored-by: Markus Pesch <markus.pesch@cryptic.systems>
Co-committed-by: Markus Pesch <markus.pesch@cryptic.systems>

README.md

@@ -33,6 +33,7 @@
 - [Metrics and profiling](#metrics-and-profiling)
   - [Secure Metrics Endpoint](#secure-metrics-endpoint)
 - [Pod annotations](#pod-annotations)
+- [TLS certificate rotation](#tls-certificate-rotation)
 - [Themes](#themes)
 - [Renovate](#renovate)
 - [Parameters](#parameters)
@@ -816,6 +817,31 @@ gitea:
   podAnnotations: {}
 ```
 
+## TLS certificate rotation
+
+If Gitea uses TLS certificates that are mounted as a secret in the container file system, Gitea will not automatically apply them when the TLS certificates are rotated.
+Such a rotation can be for example triggered, when the cert-manager issues new TLS certificates before expiring. Further information is described as GitHub
+[issue](https://github.com/go-gitea/gitea/issues/27962).
+
+Until the issue is present, a workaround can be applied.
+For example stakater's [reloader](https://github.com/stakater/Reloader) controller can be used to trigger a rolling update.
+The following annotation must be added to instruct the reloader controller to trigger a rolling update, when the mounted `configMaps` and `secrets` have been changed.
+
+```yaml
+deployment:
+  annotations:
+    reloader.stakater.com/auto: "true"
+```
+
+Instead of triggering a rolling update for configMap and secret resources, this action can also be defined for individual items.
+For example, when the secret named `gitea-tls` is mounted and the reloader controller should only listen for changes of this secret:
+
+```yaml
+deployment:
+  annotations:
+    secret.reloader.stakater.com/reload: "gitea-tls"
+```
+
 ## Themes
 
 Custom themes can be added via k8s secrets and referencing them in `values.yaml`.