Add FPGA documentation in readme

README.md

@@ -1,5 +1,9 @@
 # NixOS on RISC-V
 
+This repository contains NixOS configurations for different RISC-V machines.
+
+## QEMU
+
 To boot the system in QEMU, first enter the development shell:
 
 ```
@@ -17,3 +21,10 @@ To prevent the GC from erasing the system:
 ```
 $ nix build .#devShells.x86_64-linux.default --out-link result-env
 ```
+
+## FPGA
+
+```
+. fpga/env.sh
+fpga/fpgactl -w /path/to/bitstream -b openpiton2.bin -k kernel-nixos -r initrd-nixos
+```