Error building git repository dependency: cannot open ./project.janet when jpm install this module

jpm install Error as no project.janet existed 

```shell
Error building git repository dependency: cannot open ./project.janet
```

As no doc tells how to define a binding module which implements in c++ and need to be build on installtion. So i could not help to fix it.

Also i verified the binding logic to libui works as expected, it's cool!

Thx for all the effort of janet team.