about contains a link to the GitHub repo

[TheoPannetier]

It would fun to offer players the possibility to contribute to the game, or just see the code via a button that direct to this repo.

For this, about should contain a link to the repo, to be passed to the corresponding button in about_view

  {
    about ab;
    std::vector<std::string> link_to_gh = ab.get_link_repo();
  }