Mun uses QMK firmware. Documentation on installation, keymaps and compiling can be found here.
To install the default keymap: (LED PCBs do not need to be installed)
Install QMK Toolbox
Flash the left half
Push the slide switches into place, towards the port you want to connect to the PC. An indicator for the standard setup is on the bottom of the LED PCB.
QMK Toolbox: Choose the left firmware .bin with
Plug in the leftmost port to the PC.
Reset the board by pressing the reset switch on the PCB.
Flash: Press the flash button in QMK Toolbox.
Flash the right half
Repeat the above with the right .bin file, using the rightmost port to the PC.
Plug the leftmost port into your PC, and the two middle ports into each other.
After the initial setup, you can update your keymap using QMK Toolbox, and you only need to flash the primary half.
For custom keymaps, do the following (To be changed when Mün enters QMK master)
Install QMK MSYS and open, run the following:
git clone -b development https://github.com/rgbkb/qmk_firmware
qmk setup - press Y when asked to install submodules
qmk flash -kb rgbkb/mun -km default -bl dfu-util-split-left
Reset the board, it will flash automatically
Flash the right half with
qmk flash -kb rgbkb/mun -km default -bl dfu-util-split-right
If QMK Toolbox doesn't work, try these steps