The software (zOS) build needs zSoft and the legacy FPGA test-image Makefile
needs the ZPU SoC sources, but a user cloning the repo would not know that.
Add them as git submodules alongside the existing TZFS one, all pointing at
git.eaw.app/eaw, so a `git clone --recurse-submodules` (done by the setup
script) transparently pulls everything:
software/TZFS -> eaw/TZFS (main) - the TranZPUter Filing System
software/zSoft -> eaw/zSoft (master) - zOS/ZPUTA/IOCP (the buildable branch)
zpu -> eaw/ZPU - ZPU SoC sources for the legacy builds
Shallow-tracked to keep the checkout small.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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