Update README (add command for installing wasm on an ARM-based CPU)

Signed-off-by: Doctor K <doctor_whoami@ghostchain.io>

README.md

@@ -158,6 +158,11 @@ rustup target add wasm32-unknown-unknown --toolchain nightly
 rustup target add wasm32-unknown-unknown --toolchain stable-x86_64-unknown-linux-gnu
 ```
 
+If you are trying to install WebAssembly (wasm) on an ARM-based processor like the ones in Raspberry Pi try this instead:
+```bash
+rustup target add wasm32-unknown-unknown --toolchain stable-aarch64-unknown-linux-gnu
+```
+
 **_IF error try_**
 ```bash
 rustup target add wasm32-unknown-unknown --toolchain default