This project includes a Vagrantfile that will allow you to build a new firmware for your keyboard very easily without major changes to your primary operating system. This also ensures that when you clone the project and perform a build, you have the exact same environment as anyone else using the Vagrantfile to build. This makes it much easier for people to help you troubleshoot any issues you encounter.
Using the /Vagrantfile in this repository requires you have Vagrant as well as VirtualBox (or VMware Workstation and Vagrant VMware plugin but the (paid) VMware plugin requires a licensed copy of VMware Workstation/Fusion).
COMPATIBILITY NOTICE Certain versions of Virtualbox 5 appear to have an incompatibility with the Virtualbox extensions installed in the boxes in this Vagrantfile. If you encounter any issues with the /vagrant mount not succeeding, please upgrade your version of Virtualbox to at least 5.0.12. Alternately, you can try running the following command: vagrant plugin install vagrant-vbguest
Other than having Vagrant and Virtualbox installed and possibly a restart of your computer afterwards, you can simple run a 'vagrant up' anywhere inside the folder where you checked out this project and it will start a Linux virtual machine that contains all the tools required to build this project. There is a post Vagrant startup hint that will get you off on the right foot, otherwise you can also reference the build documentation below.
The "easy" way to flash the firmware is using a tool from your host OS:
If you want to program via the command line you can uncomment the ['modifyvm'] lines in the Vagrantfile to enable the USB passthrough into Linux and then program using the command line tools like dfu-util/dfu-programmer or you can install the Teensy CLI version.