Update docs

doc/api.rst

@@ -157,7 +157,7 @@ Output iterator support
 -----------------------
 
 .. doxygenfunction:: fmt::format_to(OutputIt, string_view, const Args&...)
-.. doxygenfunction:: fmt::format_to_n(OutputIt, size_t, string_view, const Args&...)
+.. doxygenfunction:: fmt::format_to_n(OutputIt, std::size_t, string_view, const Args&...)
 .. doxygenstruct:: fmt::format_to_n_result
    :members:
 

include/fmt/format.h

@@ -3458,6 +3458,7 @@ auto join(const Range &range, wstring_view sep)
 /**
   \rst
   Converts *value* to ``std::string`` using the default format for type *T*.
+  It doesn't support user-defined types with custom formatters.
 
   **Example**::