Install c++ manpages on ubuntu

 When you simply check the contents of c++ std api in terminal

$ man std::lock_guard                        
No manual entry for std::lock_guard

$ sudo apt install libstdc++-10-doc

$ man std::lock_guard | cat
std::lock_guard< _Mutex >(3cxx)                                                                                                                                                                                                       std::lock_guard< _Mutex >(3cxx)

NAME
       std::lock_guard< _Mutex > - A simple scoped lock type.
......