This project is already part of the official OpenWrt package feed. On your device running OpenWrt, do:
opkg update
opkg install device-observatory
The configuration file can be found in /etc/config/device-observatory.
These steps are for building an OpenWrt package (equivalent to Debian Linux .deb files) yourself.
For building OpenWrt on Debian Linux, you need to install these packages:
apt install git subversion g++ libncurses5-dev gawk zlib1g-dev build-essential
Now download OpenWrt and the package files:
git clone https://github.com/openwrt/openwrt
cd openwrt
./scripts/feeds update -a
./scripts/feeds install -a
git clone https://github.com/mwarning/device-observatory.git
cp -rf device-observatory/openwrt/device-repository package/
rm -rf device-observatory/
make menuconfig
At this point select the appropiate "Target System" and "Target Profile" depending on what target chipset/router you want to build for. Also mark the new package under "Utils" => "device-observatory".
Now build the tools/toolchain and device-repository:
make
After a successful build, the images and all *.ipk packages are now inside the bin/ folder. You can install the *.ipk file using "opkg install /tmp/<ipkg-file>" on the router.
For details please check the OpenWrt documentation.