I don’t know any tutorial but I did install syncthing on a DS214 like this:
- create user st and add to admin group to get access to all files and folders
- login to ssh as root
- switch to user st with
su -s /bin/ash st - go to home dir with
cd(which should bring you to/volume1/homes/st/ - download and extract syncthing arm version; and move syncthing binary from sub folder to home folder
- start syncthing, let it create certs and config, then kill it
- edit config to change web ui from 127.0.0.1 to 0.0.0.0
To start syncthing on boot, you can add su -s /bin/ash -c /volume1/homes/st/syncthing st to rc.local or you can create a task in synogolgy ui which executes ash su -s /bin/ash -c /volume1/homes/st/syncthing st to run it manually (disable schedule) (thats what I did)
volume1/can be different on your NAS, depending on where the user home dirs are located.