ensure_utf8() is available since v2.4.0

[zchrissirhcz]

The README.md gives the first code:

int main(int argc, char** argv) {
    CLI::App app{"App description"};
    argv = app.ensure_utf8(argv);

    std::string filename = "default";
    app.add_option("-f,--file", filename, "A help string");

    CLI11_PARSE(app, argc, argv);
    return 0;
}

And says:

For more information about 🆕ensure_utf8 the section on
Unicode support below. The 🆕ensure_utf8 function is only
available in main currently and not in a release.

But I find that v2.4.0 starts provide this funtion. Maybe the README.md can be revised? Thanks.

[phlptp]

we will be sure to update this when we get the docs finalized for the next release (likely coming soon). Thanks!