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.
     ///