Tutorial still uses old CMake generator

The Installing dependencies sections, which uses Poco example, still uses `cmake` generator. It would be nice if we could adopt `CMakeToolchain` + `CMakeDeps` by default to show a less intrusive way using Conan, no more `conan_basic_setup()` injected in user's CMake file.

https://docs.conan.io/en/latest/using_packages/conanfile_txt.html