How to integrate `cmake_find_package_multi` with CMake

Hi,

The docs state

> You also need to adjust CMAKE_PREFIX_PATH and CMAKE_MODULE_PATH so CMake can locate all the Config.cmake files: The CMAKE_PREFIX_PATH is used by the find_package and the CMAKE_MODULE_PATH is used by the find_dependency calls that locates the transitive dependencies.

However, there is no information on how to do it in the best way. It confuses people that are not CMake experts. I get questions from my students if they should do it:
- inside CMake file with `set()`
- externally with `-DCMAKE_PREFIX_PATH...`
- or maybe set some environemnt variable.

As it is going to be THE CMake generator for Conan 2.0 it would be nice to have an easy instruction to follow so people can get familiar with it more easily.