Update README with new hash functions for large objects

Added hdr::hash_grow_map_heavy and hdr::hash_grow_set_heavy for better memory usage and iteration speed.

Author: hordi

README.md

@@ -4,6 +4,8 @@ Fast C++ flat (open addressing) hash set/map header only library. Requred C++11
 Drop in replacement (mostly, references invaildated if reallocation happens, allocator-type is absent) implementation of unordered hash-set and hash-map.
 Default hash-functions use actual 32-bits hash-value, makes sense to use if amount of elements less than UINT_MAX/2 for good distribution. In other case - should be used 64-bits result hash-function (hash_set1.hpp supports full range of size_t).
 
+hdr::hash_grow_map_heavy and hdr::hash_grow_set_heavy added for big (sizeof) objects to minimize memory usage and improve iteration speed.
+
 
 EXAMPLES