Add doc for upload size limit

Author: technicalguru

README.md

@@ -75,6 +75,43 @@ You can further customize `config.inc.php`. Please follow these instructions:
 1. Customize your configuration file.
 1. Provide your customized file back into the `/var/www/html` by using a volume mapping.
 
+# Increase Upload size for attachments
+The attachment size is controlled by the PHP configuration. The file must be placed in `/usr/local/etc/php/conf.d/`:
+
+```
+upload_max_filesize = 20M
+post_max_size = 20M
+```
+
+For Kubernetes using the HELM chart, create the following ConfigMap:
+
+```
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: mailserver-roundcube-upload
+data:
+  upload.ini: |-
+    upload_max_filesize = 10M
+    post_max_size = 10M
+```
+
+Add the following lines to your HELM values.yaml file:
+
+```
+additionalContainerSpec:
+  volumeMounts:
+  - mountPath: /usr/local/etc/php/conf.d/upload.ini
+    name: roundcube-upload-config
+    subPath: upload.ini
+additionalPodSpec:
+  volumes:
+  - name: roundcube-upload-config
+    configMap:
+      name: mailserver-roundcube-upload
+```
+
+
 # Issues
 This Docker image is mature and supports my own mailserver in production. There are no known issues at the moment.