Build documentation needs to be improved

[mguthaus]

The pre-built executables don't work on many platforms (e.g. Ubuntu 20.04) due to missing dependencies, so it would be good to have some general instructions on building from source in the README.

[rnpnr]

Check the scripts directory. Its a go project so dependencies are automatically downloaded when you run go build. If you don't want to use the build_linux.sh script you can run:

go build -o out/yomichan-import yomichan/main.go

in the project root. Or change the yomichan/main.go to yomichan-gtk/main.go if you prefer the graphical version.