docs: add installation instructions for cargo-binutils

Fixes #1.

README.md

@@ -14,7 +14,12 @@
 ## Installation
 
 1. [Install `arduino-cli`](https://arduino.github.io/arduino-cli/latest/installation/)
-2. Install `arduino-run`:
+2. Install `cargo-binutils`:
+   ```
+   cargo install cargo-binutils
+   rustup component add llvm-tools
+   ```
+4. Install `arduino-run`:
     ```
     cargo install arduino-run
     ```