Add example with a bunch of leading zeos

Author: syvb

library/std/src/net/ip.rs

@@ -74,6 +74,7 @@ pub enum IpAddr {
 /// assert_eq!("127.0.0.1".parse(), Ok(localhost));
 /// assert_eq!(localhost.is_loopback(), true);
 /// assert!("012.004.002.000".parse::<Ipv4Addr>().is_err()); // all octets are in octal
+/// assert!("0000000.0.0.0".parse::<Ipv4Addr>().is_err()); // first octet is a zero in octal
 /// assert!("0xcb.0x0.0x71.0x00".parse::<Ipv4Addr>().is_err()); // all octets are in hex
 /// ```
 #[derive(Copy)]