Add C++ resource (#2903)

free-programming-books.md

@@ -929,6 +929,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [C++ Annotations](https://fbb-git.github.io/cppannotations/)
 * [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md) - Editors: Bjarne Stroustrup, Herb Sutter
 * [C++ GUI Programming With Qt 3](http://www.computer-books.us/cpp_0010.php)
+* [C++ Language](http://www.cplusplus.com/doc/tutorial/)
 * [C++ Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/cplusplus) (PDF, Kindle) (email address *requested*, not required)
 * [C++ Today](http://www.oreilly.com/programming/free/c++-today.csp) (email address *requested*, not required)
 * [C++ Tricks](http://www.bordoon.com/cplusplus/book_wrapper.html)