Fix return value comment for fwrite()

file.asm

@@ -101,7 +101,7 @@ fclose:
 	ret
 ;----- fwrite(FILE* fp, char* str) -----;
 ; writes a string to opened file
-; return value: 0 on success, below 0 otherwise (neg errno)
+; return value: amount of written characters on success, below 0 otherwise (neg errno)
 fwrite:
 	push	rbp
 	mov	rbp, rsp