Build system documentation
Summary
Most physicists aren't familiar with the usual steps involved in building software, the concepts of source/build/install locations and CMake in general. We should provide some starter-level documentation.
Mentioned in https://gitlab.cern.ch/cmsgemonline/cmsgemos/-/merge_requests/5#note_3532883
What is the expected correct behavior?
The build system is documented.
Possible fixes
Some parts could be pillaged from StackOverflow (provided that the license is compatible).