(Finsert): Mention `string-make-multibyte' and

`string-as-multibyte' in doc string.

src/editfns.c

@@ -2061,9 +2061,14 @@ Point and before-insertion markers move forward to end up
 Any other markers at the point of insertion remain before the text.
 
 If the current buffer is multibyte, unibyte strings are converted
-to multibyte for insertion (see `unibyte-char-to-multibyte').
+to multibyte for insertion (see `string-make-multibyte').
 If the current buffer is unibyte, multibyte strings are converted
-to unibyte for insertion.
+to unibyte for insertion (see `string-make-unibyte').
+
+When operating on binary data, it may be necessary to preserve the
+original bytes of a unibyte string when inserting it into a multibyte
+buffer; to accomplish this, apply `string-as-multibyte' to the string
+and insert the result.
 
 usage: (insert &rest ARGS)  */)
      (nargs, args)