(Hopefully) improve a comment about getifaddrs.

src/ifaddrs.rs

@@ -110,7 +110,9 @@ impl Iterator for InterfaceAddressIterator {
 ///
 /// Note that the underlying implementation differs between OSes. Only the
 /// most common address families are supported by the nix crate (due to
-/// lack of time and complexity of testing). For any entry not supported,
+/// lack of time and complexity of testing). The address familiy is encoded
+/// in the specific variant of `SockAddr` returned for the fields `address`,
+/// `netmask`, `broadcast`, and `destination`. For any entry not supported,
 /// the returned list will contain a `None` entry.
 ///
 /// # Example