Add missing link

Author: m0ppers

src/libstd/io/mod.rs

@@ -1506,6 +1506,8 @@ pub trait BufRead: Read {
  /// error is encountered then `buf` may contain some bytes already read in
  /// the event that all data read so far was valid UTF-8.
  ///
+ /// [`read_until`]: #method.read_until
+ ///
  /// # Examples
  ///
  /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In