I suggest that the Synology install instructions page be updated regarding the Java prerequisite.
The current suggestion to use the PC-Loadletter Repo is problematic. That tool has not been updated since January so it will install an out-of-date version of Java missing Oracle security fixes. Even worse, it installs a version of Java that will not work on certain ARMv7 machines.
My suggestion is to document the Synology maintained Java 8 package available from the Package Center on the DiskStation. After the Java 8 package is installed, open it and select the Upgrade Java box. The package will guide the user to download and install the current Oracle Java SE package appropriate for the processor of the Synology unit.