[cpp][15_bsearch] comments on IterT.

Author: Liam0205

c-cpp/15_bsearch/bsearch.hpp

@@ -10,6 +10,9 @@
 
 enum class BsearchPolicy { FIRST, LAST, UNSPECIFIED };
 
+// Liam Huang: The algorithm works right with iterators that meet the ForwardIterator requirement,
+// but with a bad time complexity. For better performance, iterators should meet
+// the RandomAccessIterator requirement.
 template <typename IterT,
  typename ValueT = typename std::iterator_traits<IterT>::value_type,
  typename Compare>