First, download the Mindustry mod-compatible version here.
Clone this repository first. Assets are in src/main/resources. Edit sprites and block names there.
mod-info.json is also in that folder. Its contents should be self-explanatory.
Make sure any content you make is prefixed with the mod name, e.g. if your mod is named blah, a new block called Sign would be called blah:sign.
Also note that all textures are prefixed with the mod name. If you have a texture in the sprites directory called sign.png, it would be fetched by calling Core.atlas.find("blah:sign").
gradlew build / ./gradlew build
Output jar should be in build/libs.
Open Mindustry, Mods -> Import Mod -> Select the jar file from the previous step.
Don't. I won't fix them.
This has been proven to work on Android, but it requires a separate compilation step, as well as a lot of messing around. Until this sytem is proven to work (or the other way around), I won't be putting any effort into an Android build.
Currently unsupported.