Need to be add-up c++ official documentation, will give you an extra edge

**This website seems like a documentation of c++. But I think its official documentation should added in this web page.**
- Like we can add--
- 1. [cplusplus.com](https://cplusplus.com/doc/).
- 2. [ISOCPP.com](https://isocpp.org/std/the-standard)
- 3. [CPPREFERENCE.com](http://cppreference.com/)

The issue does not name a file or test; start by locating the site's existing documentation or resource links. Add the three listed C++ documentation links, then verify they are visible and work from the relevant page.

Written by the indexing model from the issue text.