This readme should help you with tailscale client setup.
There are two packages related to tailscale. Tailscaled (daemon which has to run every time you want to be connected to VPN) and tailscale (package with a utility which is necessary for registering device).
To install them run
opkg install tailscale tailscaled
First, enable and run daemon
/etc/init.d/tailscale enable
/etc/init.d/tailscale start
Then you should use tailscale utility to get a login link for your device.
Run command and finish device registration with the given URL.
tailscale up
If you are running with nftables, it is not supported by tailscale, so disable it and configure firewall by yourself and add argument --netfilter-mode off to tailscale up command to disable iptables use.
After that, you should see your router in tailscale admin page.