Add doc comment and example for host module

src/host.rs

@@ -1,3 +1,16 @@
+//! This module contains a data structure representing dns
+//! hosts which can be readily parsed from or converted to strings.
+//! # Examples
+//! Parse a host from a given string
+//! ```
+//! use dory::host::Host;
+//!
+//! let host_str = "misfin.example.com";
+//! let host: Host = host_str.parse().unwrap();
+//! assert_eq!(host.subdomain.unwrap().as_str(), "misfin");
+//! assert_eq!(host.domain.as_str(), "example");
+//! assert_eq!(host.tld.as_str(), "com");
+//! ```
 use std::{fmt, str::FromStr};
 
 #[derive(Clone, Debug, Default, PartialEq)]