Clarify that format_to[_n] do not append a terminating null

include/fmt/core.h

@@ -2994,7 +2994,7 @@ auto vformat_to(OutputIt out, string_view fmt, format_args args) -> OutputIt {
  \rst
  Formats ``args`` according to specifications in ``fmt``, writes the result to
  the output iterator ``out`` and returns the iterator past the end of the output
- range.
+ range. `format_to` does not append a terminating null character.
 
  **Example**::
 
@@ -3032,6 +3032,7 @@ auto vformat_to_n(OutputIt out, size_t n, string_view fmt, format_args args)
   Formats ``args`` according to specifications in ``fmt``, writes up to ``n``
   characters of the result to the output iterator ``out`` and returns the total
   (not truncated) output size and the iterator past the end of the output range.
+  `format_to_n` does not append a terminating null character.
   \endrst
  */
 template <typename OutputIt, typename... T,