Method add_node

chapter 4/node.rs:34–39

(&self, addr: String)

    }

    pub fn add_node(&self, addr: String) {
        let mut inner = self.inner.write().unwrap();
        if let None = inner.iter().position(|x| x.get_addr().eq(addr.as_str())) {
            inner.push(Node::new(addr));
        }
    }

    pub fn evict_node(&self, addr: &str) {
        let mut inner = self.inner.write().unwrap();