fix tokio example

Cargo.toml

@@ -22,6 +22,7 @@ futures = "0.3.15"
 [dev-dependencies]
 serde_json = "1.0.62"
 futures = "0.3.15"
+tokio = { version = "1", features = ["full"] } # for example
 
 [build-dependencies]
 common = { path = "common", version = "0.0.3" }

src/lib.rs

@@ -885,6 +885,8 @@ pub struct Node {
     pubs: Vec<Arc<rcl_publisher_t>>,
 }
 
+unsafe impl Send for Node {}
+
 impl Node {
     pub fn name(&self) -> Result<String> {
         let cstr = unsafe { rcl_node_get_name(self.node_handle.as_ref()) };