You can use the offical OpenWrt snapshot (its not in main yet)
i personally like https://github.com/anaelorlinski/OpenWrt-NanoPi-R2S-R4S-Builds as he has docker built in. He also supports both the 1gb and 4gb builds. I dont know if the 1gb patch got added to OpenWrt yet. It was suppose to be upstreamed some while back but as i dont have the 1gb version its not a problem i keep an eye on.