Our README.md links to the current C++ Working Draft. The C++ Standardization Committee just released a new draft, so we should update our link.

Standardization Committees work with lots of documents, so they use "document numbers" to stay organized. The old C++ Working Draft was N4861. Our README.md mentions the document number in 3 places, all of which need to be updated to the new draft's number, N4868.

Here are the relevant lines, displayed with the Windows findstr utility:

S:\GitHub\STL>findstr /i N4861 README.md
We're implementing the latest C++ Working Draft, currently [N4861][], which will eventually become the next C++
[N4861]: https://wg21.link/n4861

This issue is intended for a new contributor (especially one new to GitHub) to get started with the simplest possible change.