Clarify docs on what IPv4 octal addresses are
Clarify docs on what IPv4 octal addresses are

The way octal literals are written in IP addresses differs from the way
they are written in Rust code, so the way that octal/hex literals in IPs
are written is explictly mentioned.

graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust