Update C++ documentation to state that C++17 is required #1053

Job	Run time
build (macos-11, tool)	2m 9s
cpp-lib-build (macos-11, clang, ON)	9m 54s
build (macos-11, cpp)	40m 38s
cpp-lib-build (macos-11, clang, OFF)	10m 55s
build (macos-11, csharp)	14m 11s
cpp-lib-build (macos-11, gcc, ON)	8m 2s
build (macos-11, dart)	6m 32s
cpp-lib-build (macos-11, gcc, OFF)	12m 2s
build (macos-11, go)	4m 39s
cpp-lib-build (ubuntu-20.04, clang, ON)	3m 25s
build (macos-11, java)	2m 8s
cpp-lib-build (ubuntu-20.04, clang, OFF)	3m 27s
build (macos-11, javascript)	3m 53s
cpp-lib-build (ubuntu-20.04, gcc, ON)	3m 3s
build (macos-11, typescript)	19m 34s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	3m 11s
build (macos-11, php)	23s
cpp-lib-build (windows-2022, clang, ON)	4m 45s
build (macos-11, python3)	2m 14s
cpp-lib-build (windows-2022, clang, OFF)	6m 6s
build (ubuntu-20.04, tool)	1m 13s
cpp-lib-build (windows-2022, cl)	4m 36s
build (ubuntu-20.04, cpp)	17m 18s
build (ubuntu-20.04, csharp)	5m 6s
build (ubuntu-20.04, dart)	3m 33s
build (ubuntu-20.04, go)	2m 18s
build (ubuntu-20.04, java)	1m 8s
build (ubuntu-20.04, javascript)	1m 23s
build (ubuntu-20.04, typescript)	9m 54s
build (ubuntu-20.04, php)	1m 47s
build (ubuntu-20.04, python3)	1m 7s
build (windows-2022, tool)	1m 34s
build (windows-2022, cpp)	22m 10s
build (windows-2022, csharp)	7m 44s
build (windows-2022, dart)	4m 25s
build (windows-2022, go)	6m 34s
build (windows-2022, java)	1m 51s
build (windows-2022, javascript)	2m 20s
build (windows-2022, typescript)	20m 26s
build (windows-2022, php)	2m 17s
build (windows-2022, python3)	1m 54s
	4h 41m 49s

Provide feedback