tree_reduce doc: fix formatting

Author: rbruenig

src/lib.rs

@@ -2536,10 +2536,10 @@ pub trait Itertools: Iterator {
  ///
  /// Moreover, the output of `tree_reduce` is preferable to that of [`Iterator::reduce`] in
  /// certain cases. For example, building a binary search tree using `tree_reduce` will result in
- /// a balanced tree with height O(ln(n)), while [`Iterator::reduce`] will output a tree with
- /// height O(n), essentially a linked list.
+ /// a balanced tree with height `O(ln(n))`, while [`Iterator::reduce`] will output a tree with
+ /// height `O(n)`, essentially a linked list.
  ///
- /// If 'f' does not benefit from such a reordering, like `u32::wrapping_add`, prefer the
+ /// If `f` does not benefit from such a reordering, like `u32::wrapping_add`, prefer the
  /// normal [`Iterator::reduce`] instead since it will most likely result in the generation of
  /// simpler code because the compiler is able to optimize it.
  ///