Extract rust snippets and reference them

snippets/rust/src/buy_btc.rs

@@ -0,0 +1,14 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use breez_sdk_core::*;
+
+async fn buy(sdk: Arc<BreezServices>) -> Result<()> {
+    let res = sdk.buy_bitcoin(
+        BuyBitcoinRequest {
+            provider: BuyBitcoinProvider::Moonpay,
+            opening_fee_params: None})
+        .await?;
+
+    Ok(())
+}