PWNCUBE firmware v6 — build dependencies

Two archives excluded from the main repository tree to keep it clone-friendly — extract them into place before building (see Firmware/docs/getting-started.en.md).

Asset	Contents	Extract to
toolchain.tar.gz	ARM (arm-rockchip830-linux-uclibcgnueabihf) + RISC-V (xpack-riscv-none-embed-gcc-10.2.0) cross-compilers. GPL-3.0/LGPL-2.1, freely redistributable.	Firmware/toolchain/
rkbin.tar.gz	Rockchip's proprietary boot-stage binaries, provided by ElectronicCats for use with this project.	Firmware/src/rkbin/

tar -xzf toolchain.tar.gz -C Firmware/
tar -xzf rkbin.tar.gz -C Firmware/src/