Add the risc-v toolchain, couldn't package it with nix sadly :/

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

flake.nix

@@ -33,6 +33,9 @@
             gcc-arm-embedded
             openocd-pico.packages.${system}.default
           ];
+          shellHook = ''
+            export PATH="$PATH:/home/jmug/dev/built-riscv-gnu-toolchain/bin"
+          '';
         };
       }
     );