keyforkd-client: add note about tests requiring multithread runner

keyforkd-client/src/tests.rs

@@ -13,7 +13,7 @@ fn secp256k1() {
         .remove(&"secp256k1".to_string())
         .unwrap();
 
-    // todo: move to tokio::sync channels to avoid using multi thread tokio
+    // note: since client is non async, can't be single threaded
     let rt = Builder::new_multi_thread().enable_io().build().unwrap();
     let tempdir = TempDir::new("keyfork-seed").unwrap();
     for (i, per_seed) in tests.into_iter().enumerate() {