see other branches for different openwrt releases(hope openwrt adds support for this device)
see chaos_calmer branch for trunk patches https://github.com/hackruu/nexx-wt1520-openwrt/tree/chaos_calmer
How to get your image:
2) extract it
3) copy files from this git-repo to your extracted directory (OpenWrt-ImageBuilder-ramips_rt305x-for-linux-x86_64)
4) edit build.sh, add/remove packages for PACKAGES variable.
5) run build.sh, it will apply patch(if needed) to current imagebuilder and build your shining firmware.