Add readme

flake.nix

@@ -14,10 +14,7 @@
       default = pkgs.mkShell {
         packages = with pkgs; [
           picotool
-          elf2uf2-rs
-          probe-rs
           rustup
-          flip-link
         ];
       };
     });

readme.md

@@ -0,0 +1,14 @@
+# Raspberry Pi Pico 2 - with Rust!
+
+You will need nix with flakes enabled. Then:
+
+```shell_session
+$ direnv allow # setup rustup and picotool
+$ rustup show # install rustc, cargo, and the pico 2 toolchain
+# plug in your pico 2 while holding the BOOTSEL button
+$ cargo run --release
+# this will probably fail the first and you will need to install whatever is missing with rustup
+# then try again
+```
+
+Have fun!

rust-toolchain.toml

@@ -0,0 +1,5 @@
+[toolchain]
+channel = "1.80"
+components = ["rustc", "cargo"]
+targets = ["thumbv8m.main-none-eabihf"]
+profile = "minimal"