RequiredBy missing in rclone-mount.service

When registering the rclone-mount.service I get this: 

> The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
> settings in the [Install] section, and DefaultInstance for template units).
> This means they are not meant to be enabled using systemctl.

Solution:
add `RequiredBy=plexmediaserver.service` to the [Install] section in rclone-mount.service