doc: #10 Document Synology permissions

README.md

@@ -37,6 +37,7 @@ I am running it in Ubuntu Server 22.04; I also tested this setup on a [Synology
     * [Free Ports 80 and 443](#free-ports-80-and-443)
     * [Install Synology WireGuard](#install-synology-wireguard)
     * [Free Port 1900](#free-port-1900)
+    * [User Permissions](#user-permissions)
     * [Synology DHCP Server and Adguard Home Port Conflict](#synology-dhcp-server-and-adguard-home-port-conflict)
   * [NFS Share](#nfs-share)
   * [Static IP](#static-ip)
@@ -341,6 +342,19 @@ Jellyfin will fail to run by default since the port 1900
 [is not free](https://lookanotherblog.com/resolve-port-1900-conflict-between-plex-and-synology/). 
 You may free it by going to  Control Panel > File Services > Advanced > SSTP > Untick `Enable Windows network discovery`.
 
+### User Permissions
+
+By default, the user and groups are set to `1000` as it is the default on Ubuntu and many other Linux distributions.
+However, that is not the case in Synology; the first user should have an ID of `1026` and a group of `100`. 
+You may check yours with `id`. 
+Update the `USER_ID` and `GROUP_ID` in `.env` with your IDs.
+Not updating them may result in [permission issues](https://github.com/AdrienPoupa/docker-compose-nas/issues/10).
+
+```
+USER_ID=1026
+GROUP_ID=100
+```
+
 ### Synology DHCP Server and Adguard Home Port Conflict
 
 If you are using the Synology DHCP Server package, it will use port 53 even if it does not need it. This is because