added comment for windows people about READFUNCTION being needed

    /* now specify which file to upload */

    curl_easy_setopt(curl, CURLOPT_READDATA, hd_src);

    /* NOTE: if you want this example to work on Windows with libcurl as a

       DLL, you MUST also provide a read callback with

       CURLOPT_READFUNCTION. Failing to do so will give you a crash since a

       DLL may not use the variable's memory when passed in to it from an app

       like this. */

    /* and give the size of the upload (optional) */

    curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE, file_info.st_size);