add development shell.nix

shell.nix

@@ -0,0 +1,16 @@
+{ }:
+let
+  pkgs = import <nixpkgs> { overlays = [ (import ./overlay.nix) ]; };
+  hx = import ./default.nix { inherit pkgs; };
+in
+  pkgs.mkShell {
+    buildInputs = [
+    	hx.binutils-riscv32 hx.binutils-riscv64 hx.gcc-riscv32 hx.gcc-riscv64 pkgs.rustc pkgs.cargo hx.rust-riscv32i-crates
+    	(pkgs.python3.withPackages(ps: [hx.nmigen hx.nmigen-boards hx.heavycomps hx.minerva]))
+    	pkgs.yosys
+      pkgs.nextpnr
+      pkgs.trellis
+      pkgs.openocd
+    ];
+    RUSTFLAGS="-L ${hx.rust-riscv32i-crates}/lib/rustlib/riscv32i-unknown-none-elf/lib -C linker=riscv32-unknown-elf-ld -C link-arg=-Tlink.x";
+  }