chore: update README instructions for new version of bitnami helm chart (#318)

allow third images to be deployed by the chart, related to
bitnami/charts#30850 and
https://camunda.slack.com/archives/C03UR0V2R2M/p1741002015819099

Author: leiicamundi

README.md

@@ -96,6 +96,12 @@ externalDatabase:
   port: 5432
   user: keycloak
   database: keycloak
+
+global:
+  security:
+    # The following parameter is required due to https://github.com/bitnami/charts/issues/30850
+    # It does not lower security, as it only allows forks of Bitnami images, such as this one, to be deployed by the chart.
+    allowInsecureImages: true
 ```
 
 Feel free to adjust the values according to your actual configuration.