update README

README.md

@@ -341,6 +341,8 @@ using student = std::tuple<std::string, void, float>;
 // returns std::tuple<std::string, float>
 auto [name, grade] = p.get_next<student>();
 ```
+Values can also be converted to **std::string_view**. It is more efficient then converting values to **std::string** but one must be careful with the lifetime of it.
+
 To ignore a whole row, **ignore_next** could be used, returns **false** if **eof**: 
 ```cpp
 bool parser::ignore_next();