Doc update

Author: danielaparker

README.md

@@ -274,7 +274,7 @@ int main()
 
     json another_array = json::array(); 
     another_array.emplace_back(byte_string({'P','u','s','s'}),
-                               byte_string_chars_format::base64); // suggested conversion to base64
+                               semantic_tag_type::base64); // suggested conversion to base64
     another_array.emplace_back("273.15", semantic_tag_type::big_decimal);
     another_array.emplace(another_array.array_range().begin(),"bar"); // place at front